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Excited States (excited + states)
Kinds of Excited States Selected AbstractsTheoretical Studies on Metal,Metal Interaction and Intrinsic 1,3[,*(d),(s/p)] Excited States of Dinuclear d10 Complexes with Bridging Phosphane LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2006Qing-Jiang Pan Abstract To explore the metal,metal interaction and spectroscopic properties, the ground- and excited-state structures of [M2(dpm)2]2+ [M = Ag (2), Cu (3), dpm = bis(diphosphanyl)methane] and their solvated species [M2(dpm)2]2+·(MeCN)2 were optimized by the MP2 and CIS methods, respectively. In the ground states, the calculated M,M distances and their corresponding M,M stretching frequencies for 2 and 3 indicate the presence of metallophilic attraction; there is strong N,Cu/Ag coordination in acetonitrile, which is different from the case in previous studies of [Au2(dpm)2]2+ (1). CIS calculations show that 2 and 3 have 1,3[,*(d),(s/p)] as their lowest-energy excited state, as is also the case for 1, confirmed by unrestricted MP2 calculations. On the basis of the CIS-optimized structures, the TD-DFT (B3LYP) method was employed to calculate the emission spectra of such complexes. For 3, the phosphorescent emissions were calculated at 424 and 514 nm in the solid state and acetonitrile, which is comparable to the experimental data of 475 and 480 nm, respectively. The comparison between the gas-phase and solution emissions for 1,3 reveals that the N,M coordination results in a large red-shift of the emission wavelength. Taking previous studies into account , we found that the M,M distances are linearly correlated with the M,M stretching frequencies for the dinuclear d10 complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Systematic Studies on Photoluminescence of Oligo(arylene-ethynylene)s: Tunability of Excited States and Derivatization as Luminescent Labeling Probes for ProteinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2006Yong-Gang Zhi Abstract Functionalized oligo(phenylene-ethynylene)s (OPEs) with different conjugation lengths, p -X(C6H4C,C)nSiMe3 (n = 1,4; X = NH2, NMe2, H) were synthesized by Sonogashira coupling of (phenylene-ethynylene)s and 1-iodo-4-(trimethylsilylethynyl)benzene, followed by desilylation of the p -substituted (trimethylsilylethynyl)benzenes with potassium hydroxide. The photoluminescent properties for the OPE series with different chain lengths and their solvatochromic responses were examined. The absorption maxima were red-shifted with increasing numbers of ,(C6H4C,C), units (n), and a linear plot of the absorption energy maxima vs. 1/n was obtained for each series. The emission spectra in dichloromethane showed a broad and structureless band, the energies of which (in wavenumbers) also fit linearly with 1/n. Both the absorption and emission wavelength maxima of the NH2 - and NMe2 -substituted OPEs exhibited significant solvent dependence, whereas the parent OPEs (X = H) showed only minor shifts of the ,max values in different solvents. Substituent effects upon the photoluminescent characteristics of the OPEs and the tunability of the excited states were examined with the p -X(C6H4C,C)nSiMe3 (n = 2, 3; X = NH2, NMe2, H, SMe, OMe, OH, and F) series. The H- and F-substituted counterparts exhibited high-energy vibronically structured emissions attributed to the 3(,,*) excited states of the (arylene-ethynylene) backbone. For compounds bearing NH2 and NMe2 groups, a broad red-shifted emission with a remarkable Stokes shift from the respective absorption maximum was observed, which can be assigned to an n , ,* transition. The n , ,* assignment was supported by MO calculations on the model compounds p -X(C6H4C,C)2SiH3 (X = NH2, H). Functionalization of the oligo(arylene-ethynylene)s with the N -hydroxysuccinimidyl (NHS) moiety enabled covalent attachment of the fluorophore to HSA protein molecules. A series of fluorescent labels, namely p -X(C6H4C,C)nC6H4NHS, (n = 1, X = NH2, NMe2, SMe, OMe, OH, F; n = 2, X = NH2, NMe2) and p -Me2NC6H4C,C(C4H2S)C,CC6H4NHS were synthesized, and their conjugates with HSA (human serum albumin) were characterized by MALDI-TOF mass spectrometry, UV/Vis absorption spectroscopy, and gel electrophoresis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Development of Bacteriorhodopsin Analogues and Studies of Charge Separated Excited States in the Photoprocesses of Linear Polyenes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2007Anil K. Singh Development of bacteriorhodopsin (bR) analogues employing chromophore substitution technique for the purpose of characterizing the binding site of bR and generating bR analogues with novel opto-electronic properties for applications as photoactive element in nanotechnical devices are described. Additionally, the photophysical and photochemical properties of variously substituted diarylpolyenes as models of photobiologically relevant linear polyenes are discussed. The role of charge separated dipolar excited states in the photoprocesses of linear polyenes is highlighted. [source] Synthetically Tailored Excited States: Phosphorescent, Cyclometalated Iridium(III) Complexes and Their ApplicationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2006Michael S. Lowry Abstract Phosphorescent iridium(III) complexes are being widely explored for their utility in diverse photophysical applications. The performance of these materials in such roles depends heavily on their excited-state properties, which can be tuned through ligand and substituent effects. This concept article focuses on methods for synthetically tailoring the properties of bis-cyclometalated iridium(III) materials, and explores the factors governing the nature of their lowest excited state. [source] Ultrafast Relaxation Dynamics of the Excited States of 1-Amino- and 1-(N,N -Dimethylamino)-fluoren-9-onesCHEMPHYSCHEM, Issue 17 2009Mahendra Varne Abstract The dynamics of the excited states of 1-aminofluoren-9-one (1AF) and 1-(N,N -dimethylamino)-fluoren-9-one (1DMAF) are investigated by using steady-state absorption and fluorescence as well as subpicosecond time-resolved absorption spectroscopic techniques. Following photoexcitation of 1AF, which exists in the intramolecular hydrogen-bonded form in aprotic solvents, the excited-state intramolecular proton-transfer reaction is the only relaxation process observed in the excited singlet (S1) state. However, in protic solvents, the intramolecular hydrogen bond is disrupted in the excited state and an intermolecular hydrogen bond is formed with the solvent leading to reorganization of the hydrogen-bond network structure of the solvent. The latter takes place in the timescale of the process of solvation dynamics. In the case of 1DMAF, the main relaxation pathway for the locally excited singlet, S1(LE), or S1(ICT) state is the configurational relaxation, via nearly barrierless twisting of the dimethylamino group to form the twisted intramolecular charge-transfer, S1(TICT), state. A crossing between the excited-state and ground-state potential energy curves is responsible for the fast, radiationless deactivation and nonemissive character of the S1(TICT) state in polar solvents, both aprotic and protic. However, in viscous but strong hydrogen-bond-donating solvents, such as ethylene glycol and glycerol, crossing between the potential energy surfaces for the ground electronic state and the hydrogen-bonded complex formed between the S1(TICT) state and the solvent is possibly avoided and the hydrogen-bonded complex is weakly emissive. [source] Calculated Electron Impact Ionization Cross Sections of Excited Ne Atoms Using the DM FormalismCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7 2005H. Deutsch Abstract We used the semi-classical Deutsch-Märk (DM) formalism to calculate absolute electron-impact ionization cross sections of excited Ne atoms from threshold to 1000 eV. Excited states of Ne where the outermost valence electron is excited to states with principal quantum numbers up to n = 7 and orbital angular momentum quantum numbers up to l = 2 have been considered and systematic trends in the calculated cross section data are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of excited-state properties of fluorene,thiophene oligomers by the SAC-CI theoretical approachJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2010Potjaman Poolmee Abstract Excited states of fluorene-ethylenedioxythiophene (FEDOT) and fluorene- S,S -dioxide-thiophene (FTSO2) monomers and dimers were studied by the symmetry-adapted cluster (SAC)-configuration interaction (CI) method. The absorption and emission peaks observed in the experimental spectra were theoretically assigned. The first three excited states of the optimized conformers, and the conformers of several torsional angles, were computed by SAC-CI/D95(d). Accurate absorption spectra were simulated by taking the thermal average for the conformers of torsional angles from 0° to 90°. The conformers of torsional angles 0°, 15°, and 30° mainly contributed to the absorption spectra. The full width at half-maximum of the FEDOT absorption band is 0.60 eV (4839 cm,1), which agrees very well with the experimental value of 0.61 eV (4900 cm,1). The maximum absorption wavelength is located at 303 nm, which is close to those of the experimental band (327 nm). The calculated absorption spectrum of FTSO2 showed two bands in the range of 225,450 nm. This agrees very well with the available experimental spectrum of a polymer of FTSO2, where two bands are detected. The excited-state geometries were investigated by CIS/6-31G(d). These showed a quinoid-type structure which exhibited a shortening of the inter-ring distance (0.06 Å for FEDOT and 0.04 Å for FTSO2). The calculated emission energy of FEDOT is 3.43 eV, which agrees very well with the available experimental data (3.46 eV). The fwhmE is about 0.49 eV (3952 cm,1), while the experimental fwhm is 0.43 eV (3500 cm,1). For FTSO2, two bands were also found in the emission spectrum. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Excited states of OsO4: A comprehensive time-dependent relativistic density functional theory studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2010Yong Zhang Abstract A large number of scalar as well as spinor excited states of OsO4, in the experimentally accessible energy range of 3,11 eV, have been captured by time-dependent relativistic density functional linear response theory based on an exact two-component Hamiltonian resulting from the symmetrized elimination of the small component. The results are grossly in good agreement with those by the singles and doubles coupled-cluster linear response theory in conjunction with relativistic effective core potentials. The simulated-excitation spectrum is also in line with the available experiment. Furthermore, combined with detailed analysis of the excited states, the nature of the observed optical transitions is clearly elucidated. It is found that a few scalar states of 3T1 and 3T2 symmetries are split significantly by the spin-orbit coupling. The possible source for the substantial spin-orbit splittings of ligand molecular orbitals is carefully examined, leading to a new interpretation on the primary valence photoelectron ionization spectrum of OsO4. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Excited states and spontaneous transition lifetimes of donor impurities in quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007G. Murillo Abstract We calculate the 2p,1s-like transition energy and the spontaneous lifetime of an on-center shallow donor impurity in a spherical parabolic GaAs-(Ga,Al)As quantum dot (PQD) as a function of the radius of the structure and the strength of an applied electric field. In our calculations we use a variational method, within the effective mass and dipolar approximations. We find that the spontaneous lifetimes increase with the radius of the PQD and the applied electric field. In this direction our results revel that the electric field can be used to suppress the electron-phonon interaction driving to the increasing of the 2p-1s spontaneous life-time, showing the feasibility of using impurity states to be used in quantum computing developments. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spectroscopic Diagnostics of Pulsed arc Plasmas for Particle GenerationCONTRIBUTIONS TO PLASMA PHYSICS, Issue 8 2008K. Behringer Abstract Pulsed arc plasmas were diagnosed by means of emission spectroscopy. A capacitor was discharged through argon and hydrogen leading to a few cycles of damped current oscillation with ,120 ,s period and 5-12 kA maximum current. Spectroscopic measurements in the visible range were carried out in order to characterise the electron temperature and density in the arc channel as well as electron and gas temperatures in the afterglow plasmas. Spectra were integrated over 10 ,s time windows and shifted in time from pulse to pulse. The plasmas also contained substantial fractions of electrode material (brass), namely copper and zinc. The electron density was measured in the conventional way from the broadening of H, or from the Ar I Stark width. In the arc channel, it ranged from about 3 · 1022 to 2 · 1023 m,3. The broadening of Zn II lines could also be used. Ratios of Ar I to Ar II and of Zn I to Zn II line intensities were analysed for the electron temperature. Line pairs were found which lay conveniently close in one frame of the spectrometer allowing automatic on-line analysis without relying on reproducibility. Atomic physics models including opacity were developed for Ar II and Zn II in order to check the existence of a Boltzmann distribution of their excited states. These calculations showed that the observed levels were in fact close to thermodynamic equilibrium, in particular, if the resonance lines were optically thick. Electron temperature measurements yielded values between 14000 K and 21000 K. The gas temperature in the afterglow, where particles should have formed, was derived from the rotational and vibrational temperatures of C2 molecular bands. Ratios between Cu I line intensities yielded the electron temperatures. Both were found to be a few 1000 K. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Elementary Many-Particle Processes in Plasma MicrofieldsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3 2006M. Yu. Abstract The effect of electric and magnetic plasma microfields on elementary many-body processes in plasmas is considered. As detected first by Inglis and Teller in 1939, the electric microfield controls several elementary processes in plasmas as transitions, line shifts and line broadening. We concentrate here on the many-particle processes ionization, recombination, and fusion and study a wide area of plasma parameters. In the first part the state of art of investigations on microfield distributions is reviewed in brief. In the second part, various types of ionization processes are discussed with respect to the influence of electric microfields. It is demonstrated that the processes of tunnel and rescattering ionization by laser fields as well as the process of electron collisional ionization may be strongly influenced by the electric microfields in the plasma. The third part is devoted to processes of microfield action on fusion processes and the effects on three-body recombination are investigated. It is shown that there are regions of plasma densities and temperatures, where the rate of nuclear fusion is accelerated by the electric microfields. This effect may be relevant for nuclear processes in stars. Further, fusion processes in ion clusters are studied. Finally we study in this section three-body recombination effects and show that an electric microfield influences the three-body electron-ion recombination via the highly excited states. In the fourth part, the distribution of the magnetic microfield is investigated for equilibrium, nonequilibrium, and non-uniform magnetized plasmas. We show that the field distribution in a neutral point of a non-relativistic ideal equilibrium plasma is similar to the Holtsmark distribution for the electrical microfield. Relaxation processes in nonequilibrium plasmas may lead to additional microfields. We show that in turbulent plasmas the broadening of radiative electron transitions in atoms and ions, without change of the principle quantum number, may be due to the Zeeman effect and may exceed Doppler and Stark broadening as well. Further it is shown that for optical radiation the effect of depolarization of a linearly polarized laser beams propagating through a magnetized plasma may be rather strong. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spectroscopy of High-Energy States of Lanthanide IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2010Michael F. Reid Abstract We discuss recent progress and future prospects for the analysis of the 4fN,15d excited states of lanthanide ions in host materials. We demonstrate how ab initio calculations for Ce3+ in LiYF4 may be used to estimate crystal-field and spin-orbit parameters for the 4f1 and 5d1 configurations. We show how excited-state absorption may be used to probe the electronic and geometric structure of the 4fN,15d excited states in more detail and we illustrate the possibilities with calculations for Yb2+ ions in SrCl2. [source] Systematic Studies on Photoluminescence of Oligo(arylene-ethynylene)s: Tunability of Excited States and Derivatization as Luminescent Labeling Probes for ProteinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2006Yong-Gang Zhi Abstract Functionalized oligo(phenylene-ethynylene)s (OPEs) with different conjugation lengths, p -X(C6H4C,C)nSiMe3 (n = 1,4; X = NH2, NMe2, H) were synthesized by Sonogashira coupling of (phenylene-ethynylene)s and 1-iodo-4-(trimethylsilylethynyl)benzene, followed by desilylation of the p -substituted (trimethylsilylethynyl)benzenes with potassium hydroxide. The photoluminescent properties for the OPE series with different chain lengths and their solvatochromic responses were examined. The absorption maxima were red-shifted with increasing numbers of ,(C6H4C,C), units (n), and a linear plot of the absorption energy maxima vs. 1/n was obtained for each series. The emission spectra in dichloromethane showed a broad and structureless band, the energies of which (in wavenumbers) also fit linearly with 1/n. Both the absorption and emission wavelength maxima of the NH2 - and NMe2 -substituted OPEs exhibited significant solvent dependence, whereas the parent OPEs (X = H) showed only minor shifts of the ,max values in different solvents. Substituent effects upon the photoluminescent characteristics of the OPEs and the tunability of the excited states were examined with the p -X(C6H4C,C)nSiMe3 (n = 2, 3; X = NH2, NMe2, H, SMe, OMe, OH, and F) series. The H- and F-substituted counterparts exhibited high-energy vibronically structured emissions attributed to the 3(,,*) excited states of the (arylene-ethynylene) backbone. For compounds bearing NH2 and NMe2 groups, a broad red-shifted emission with a remarkable Stokes shift from the respective absorption maximum was observed, which can be assigned to an n , ,* transition. The n , ,* assignment was supported by MO calculations on the model compounds p -X(C6H4C,C)2SiH3 (X = NH2, H). Functionalization of the oligo(arylene-ethynylene)s with the N -hydroxysuccinimidyl (NHS) moiety enabled covalent attachment of the fluorophore to HSA protein molecules. A series of fluorescent labels, namely p -X(C6H4C,C)nC6H4NHS, (n = 1, X = NH2, NMe2, SMe, OMe, OH, F; n = 2, X = NH2, NMe2) and p -Me2NC6H4C,C(C4H2S)C,CC6H4NHS were synthesized, and their conjugates with HSA (human serum albumin) were characterized by MALDI-TOF mass spectrometry, UV/Vis absorption spectroscopy, and gel electrophoresis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Efficient and Long-Living Light-Emitting Electrochemical CellsADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Rubén D. Costa Abstract Three new heteroleptic iridium complexes that combine two approaches, one leading to a high stability and the other yielding a high luminescence efficiency, are presented. All complexes contain a phenyl group at the 6-position of the neutral bpy ligand, which holds an additional, increasingly bulky substituent on the 4-position. The phenyl group allows for intramolecular ,,, stacking, which renders the complex more stable and yields long-living light-emitting electrochemical cells (LECs). The additional substituent increases the intersite distance between the cations in the film, reducing the quenching of the excitons, and should improve the efficiency of the LECs. Density functional theory calculations indicate that the three complexes have the desired ,,, intramolecular interactions between the pendant phenyl ring of the bpy ligand and the phenyl ring of one of the ppy ligands in the ground and the excited states. The photoluminescence quantum efficiency of concentrated films of the complexes improves with the increasing size of the bulky groups indicating that the adopted strategy for improving the efficiency is successful. Indeed, LEC devices employing these complexes as the primary active component show shorter turn-on times, higher efficiencies and luminances, and, surprisingly, also demonstrate longer device stabilities. [source] Magnetic-Field Effects in Organic Semiconducting Materials and DevicesADVANCED MATERIALS, Issue 14-15 2009Bin Hu Abstract It has been experimentally discovered that a low magnetic field (less than 500 mT) can substantially change the electroluminescence, photoluminescence, photocurrent, and electrical-injection current in nonmagnetic organic semiconducting materials, leading to magnetic-field effects (MFEs). Recently, there has been significant driving force in understanding the fundamental mechanisms of magnetic responses from nonmagnetic organic materials because of two potential impacts. First, MFEs can be powerful experimental tools in revealing and elucidating useful and non-useful excited processes occurring in organic electronic, optical, and optoelectronic devices. Second, MFEs can lead to the development of new multifunctional organic devices with integrated electronic, optical, and magnetic properties for energy conversion, optical communication, and sensing technologies. This progress report discusses magnetically sensitive excited states and charge-transport processes involved in MFEs. The discussions focus on both fundamental theories and tuning mechanisms of MFEs in nonmagnetic organic semiconducting materials. [source] Electron invariants and excited state structural analysis for electronic transitions within CIS, RPA, and TDDFT modelsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2010A. V. Luzanov Abstract We revisit the interpretative scheme (Luzanov et al., Theor Exp Chem 1974, 10, 354) of singly excited configuration interaction (CIS) model given earlier at semiempirical level. Detailed computations and spectral (natural orbital) treatment of the CIS density matrices of various types are presented. The corresponding hole-particle densities and related excitation localization indices are described. All the quantities are extended to the excited states calculated in the random phase approximation and closely related time-dependent density functional theory (TDDFT). The localization indices and charge transfer numbers which are invoked to describe interfragment interactions provide a basis for our scheme which is referred to as the excited state structural analysis for electronic transitions. The proposed analysis is exemplified by various moderate and large-size conjugated molecules treated within ab initio TDDFT and the Parizer,Parr,Pople approximation. Finally, we propose a possible generalization to the electronic transitions between CIS-like states followed by applications to singlet organic biradicals treated within the ,-electron spin-flip CIS. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] The electronically excited states of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine): Vertical excitationsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2009Itamar Borges Jr Abstract The RDX molecule, hexahydro-1,3,5-trinitro-1,3,5-triazine, is a key component for several energetic materials, which have important practical applications as explosives. A systematic study of the electronic excited states of RDX in gas phase using time-dependent density functional theory (TDDFT), algebraic diagrammatic construction through second order method [ADC (2)], and resolution of the identity coupled-cluster singles and doubles method (RI-CC2) was carried out. Transition energies and optical oscillator strengths were computed for a maximum of 40 transitions. RI-CC2 and ADC (2) predict a spectrum shaped by three intense ,-,* transitions, two with charge transfer and one with localized character. TDDFT fails in the description of the charge transfer states. The low-energy band of the experimental UV spectrum of RDX is assigned to the first charge transfer state. Two alternative assignments of the high-energy band are proposed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] The chemiionization reactions Ce + O and Ce + O2: Assignment of the observed chemielectron bandsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2009Tanya K. Todorova Abstract Multiconfigurational quantum chemical methods (CASSCF/CASPT2) have been used to study the chemiionization reactions Ce + O , CeO+ + e, and Ce + O2 , CeO + e,. Selected spectroscopic constants for CeOn and CeO (n = 1, 2), as well as reaction enthalpies of the chemiionization reactions of interest, have been computed and compared with experimental values. In contrast to the lanthanum case, for both Ce + O2(X3,) and Ce + O2( a1,g), the Ce + O2 , CeO + e, reaction is shown to be exothermic, and thus, contributes to the experimental chemielectron spectra. The apparent discrepancy between the computed reaction enthalpies and the high kinetic energy offset values measured in the chemielectron spectra is rationalized by arguing that chemielectrons are produced mainly via two sequential reactions (Ce + O2 , CeO + O, followed by Ce + O , CeO+ + e,) as in the case of lanthanum. For Ce + O2 (a1,g), a chemielectron band with higher kinetic energy than that recorded for Ce + O2( X3,) is obtained. This is attributed to production of O( 1D) from the reaction Ce + O2( a1,g) , CeO + O( 1D), followed by chemiionization via the reaction Ce + O( 1D) , CeO+ + e,. Accurate potential energy curves for the ground and a number of excited states of CeO and CeO+ have been computed, and a mechanism for the chemiionization reactions investigated experimentally was proposed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1,5)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009Jinglai Zhang Abstract The density functional theory (DFT) and the complete active space self-consistent-field (CASSCF) method have been used for full geometry optimization of carbon chains C2nH+ (n = 1,5) in their ground states and selected excited states, respectively. Calculations show that C2nH+ (n = 1,5) have stable linear structures with the ground state of X3, for C2H+ or X3,, for other species. The excited-state properties of C2nH+ have been investigated by the multiconfigurational second-order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low-lying states in C2nH+ (n = 1,5). Present results indicate that the predicted vertical excitation and emission energies of C2nH+ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Vibrational,rotational energies of all H2 isotopomers using Monte Carlo methodsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2006S. A. Alexander Abstract Using variational Monte Carlo techniques, we have computed several of the lowest rotational,vibrational energies of all the hydrogen molecule isotopomers (H2, HD, HT, D2, DT, and T2). These calculations do not require the excited states to be explicitly orthogonalized. We have examined both the usual Gaussian wave function form as well as a rapidly convergent Padé form. The high-quality potential energy surfaces used in these calculations are taken from our earlier work and include the Born,Oppenheimer energy, the diagonal correction to the Born,Oppenheimer approximation, and the lowest-order relativistic corrections at 24 internuclear points. Our energies are in good agreement with those determined by other methods. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Computational study of titanium (IV) complexes with organic chromophoresINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2006Ivan Kondov Abstract A computational study of small titanium complexes with the chromophores catechol, alizarin, and coumarin 343 is presented. Employing density functional theory (DFT), the ground-state geometries, energies, and harmonic frequencies of the different compounds are calculated. Furthermore, time-dependent DFT and the configuration interaction singles (CIS) method are used to determine excitation energies and excited-state gradients. Based on these results, the character of the excited states as well as electronic-vibrational coupling strengths are analyzed, and the implications for electron-transfer reactions at dye,semiconductor interfaces are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Theory of tip-dependent imaging of adsorbates in the STM: CO on Cu(111)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2006D. Drakova Abstract The processes of local electron injection or extraction in the scanning tunneling microscopy (STM) and spectroscopy (STS) lead to the creation of short-lived excited states localized at the electrode surfaces. The dynamic relaxation of the transient negative or positive ion resonances, due to both local and long-range interactions, is the clue to the understanding of numerous phenomena in STM/STS ranging from the "anomalously" large tip height corrugation amplitudes on clean metal surfaces to the observation of quantum mirages and features in the STS, which are not observed with the help of other surface spectroscopies. Quantum nanodynamics theory (QND) has been applied to calculate the interaction potential of a single CO molecule with the Cu(111) surface, with a transient negative ion resonance formed when an electron is injected from the tip, and the tunneling conductance on the clean and CO covered Cu(111) surface using a clean metal tip Al/Al(111) and a Pt(111) tip with an adsorbed CO molecule at the apex. Within QND and three-dimensional scattering theory, regarding the tunneling as an excited-state problem, we provide the explanation of the tip-dependent STM image of a single CO molecule on Cu(111). The appearance of the CO molecule as an indentation, using a clean metal tip and as a protrusion with a tip terminated by a CO molecule, is understood as a result of tunneling through two competing channels. Tunneling via adsorbate-induced ion resonances enhances the tunneling conductance. In contrast, tunneling via metal ion resonances only leads to attenuation of the conductance in the presence of the adsorbate. The current in the vicinity of the adsorbed CO molecule is reduced when a clean metal tip is used; i.e., CO appears dark in the STM image, because metal ion resonances on Cu(111) derive from the surface states with image state components coupling to plasmons and are therefore very diffuse. With a CO-terminated tip, the major current channel is, for symmetry reasons, from the 2,-derived orbital of the tip CO molecule, via the diffuse 2,-derived orbital of the CO molecule on the sample, hence adsorbed CO appears bright. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] DFT calculations of light-induced excited states and comparison with time-resolved crystallographic resultsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Philip Coppens Abstract DFT calculations of the ground and first excited states of several transition metal complexes have been performed to complement time-resolved diffraction experiments. The results from different functionals and relativistic treatments are tested against both diffraction and spectroscopic values. Calculations of the d8,d8 complex [Pt2(pyrophosphite)4]4, quantitatively reproduce metal,metal shortening on excitation to the triplet state and support bond formation between the two metal centers, as do calculations on [Rh2(1,3-diisocyanopropane)4]2+. Results on homoleptic and heteroleptic copper(I) 2,9-dimethyl,1,10-phenanthroline (dmp) complexes, which are investigated because of their potential for solar energy capture, confirm considerable molecular deformations on excitation. The distortion calculated for the isolated complex [Cu(dmp)(dmpe)]+ (dmpe=1,2-bis(dimethylphosphino)ethane) is significantly larger than observed in the crystal, indicating the constraining effect of the crystalline environment. The change in the net charge of the Cu atom upon photo-induced metal-to-ligand charge transfer is less than 0.2 e, showing the limitations of the formal Cu(I),Cu(II) designation. Electron density difference maps show a pronounced change in electronic structure of the Cu atom on excitation. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Bond length features of linear carbon chains of finite to infinite size: Visual interpretation from Pauling bond ordersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2003Zexing Cao Abstract Schemes for Kekulé structure counting of linear carbon chains are suggested. Mathematical formulas, which calculate the Pauling bond order P(k, N) of a chemical bond numbered by k, are given for the carbon chain with N carbon atoms. By use of the least-squares fitting of a linearity, relationships between Pauling bond orders and bond lengths are obtained, and such correlation of the Pauling bond order,bond length can be qualitatively extended to the excited states. The relative magnitudes of Pauling bond orders in unsaturated carbon chains dominate C,C bond lengths a well as the bond length feature with the chain size increasing. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 144,149, 2003 [source] Time asymmetry, nonexponential decay, and complex eigenvalues in the theory and computation of resonance statesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2002Cleanthes A. Nicolaides Abstract Stationary-state quantum mechanics presents no difficulties in defining and computing discrete excited states because they obey the rules established in the properties of Hilbert space. However, when this idealization has to be abandoned to formulate a theory of excited states dissipating into a continuous spectrum, the problem acquires additional interest in many fields of physics. In this article, the theory of resonances in the continuous spectrum is formulated as a problem of decaying states, whose treatment can entail time-dependent as well as energy-dependent theories. The author focuses on certain formal and computational issues and discusses their application to polyelectronic atomic states. It is argued that crucial to the theory is the understanding and computation of a multiparticle localized wavepacket, ,0, at t = 0, having a real energy E0. Assuming this as the origin, without memory of the excitation process, the author discusses aspects of time-dependent dynamics, for t , 0 as well as for t , ,, and the possible significance of nonexponential decay in the understanding of timeasymmetry. Also discussed is the origin of the complex eigenvalue Schrödinger equation (CESE) satisfied by resonance states and the state-specific methodology for its solution. The complex eigenvalue drives the decay exponentially, with a rate ,, to a good approximation. It is connected to E0 via analytic continuation of the complex self-energy function, A(z), (z is complex), into the second Riemann sheet, or, via the imposition of outgoing wave boundary conditions on the stationary state Schrödinger equation satisfied by the Fano standing wave superposition in the vicinity of E0. If the nondecay amplitude, G(t), is evaluated by inserting the unit operator I = ,dE|E> Investigation of excited-state properties of fluorene,thiophene oligomers by the SAC-CI theoretical approachJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2010Potjaman Poolmee Abstract Excited states of fluorene-ethylenedioxythiophene (FEDOT) and fluorene- S,S -dioxide-thiophene (FTSO2) monomers and dimers were studied by the symmetry-adapted cluster (SAC)-configuration interaction (CI) method. The absorption and emission peaks observed in the experimental spectra were theoretically assigned. The first three excited states of the optimized conformers, and the conformers of several torsional angles, were computed by SAC-CI/D95(d). Accurate absorption spectra were simulated by taking the thermal average for the conformers of torsional angles from 0° to 90°. The conformers of torsional angles 0°, 15°, and 30° mainly contributed to the absorption spectra. The full width at half-maximum of the FEDOT absorption band is 0.60 eV (4839 cm,1), which agrees very well with the experimental value of 0.61 eV (4900 cm,1). The maximum absorption wavelength is located at 303 nm, which is close to those of the experimental band (327 nm). The calculated absorption spectrum of FTSO2 showed two bands in the range of 225,450 nm. This agrees very well with the available experimental spectrum of a polymer of FTSO2, where two bands are detected. The excited-state geometries were investigated by CIS/6-31G(d). These showed a quinoid-type structure which exhibited a shortening of the inter-ring distance (0.06 Å for FEDOT and 0.04 Å for FTSO2). The calculated emission energy of FEDOT is 3.43 eV, which agrees very well with the available experimental data (3.46 eV). The fwhmE is about 0.49 eV (3952 cm,1), while the experimental fwhm is 0.43 eV (3500 cm,1). For FTSO2, two bands were also found in the emission spectrum. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Excited states of OsO4: A comprehensive time-dependent relativistic density functional theory studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2010Yong Zhang Abstract A large number of scalar as well as spinor excited states of OsO4, in the experimentally accessible energy range of 3,11 eV, have been captured by time-dependent relativistic density functional linear response theory based on an exact two-component Hamiltonian resulting from the symmetrized elimination of the small component. The results are grossly in good agreement with those by the singles and doubles coupled-cluster linear response theory in conjunction with relativistic effective core potentials. The simulated-excitation spectrum is also in line with the available experiment. Furthermore, combined with detailed analysis of the excited states, the nature of the observed optical transitions is clearly elucidated. It is found that a few scalar states of 3T1 and 3T2 symmetries are split significantly by the spin-orbit coupling. The possible source for the substantial spin-orbit splittings of ligand molecular orbitals is carefully examined, leading to a new interpretation on the primary valence photoelectron ionization spectrum of OsO4. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Thermodynamic calculations for molecules with asymmetric internal rotors.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2008Abstract The thermodynamic properties of three halocarbon molecules relevant in atmospheric and public health applications are presented from ab initio calculations. Our technique makes use of a reaction path-like Hamiltonian to couple all the vibrational modes to a large-amplitude torsion for 1,2-difluoroethane, 1,2-dichloroethane, and 1,2-dibromoethane, each of which possesses a heavy asymmetric rotor. Optimized ab initio energies and Hessians were calculated at the CCSD(T) and MP2 levels of theory, respectively. In addition, to investigate the contribution of electronically excited states to thermodynamic properties, several excited singlet and triplet states for each of the halocarbons were computed at the CASSCF/MRCI level. Using the resulting potentials and projected frequencies, the couplings of all the vibrational modes to the large-amplitude torsion are calculated using the new STAR-P 2.4.0 software platform that automatically parallelizes our codes with distributed memory via a familiar MATLAB interface. Utilizing the efficient parallelization scheme of STAR-P, we obtain thermodynamic properties for each of the halocarbons, with temperatures ranging from 298.15 to 1000 K. We propose that the free energies, entropies, and heat capacities obtained from our methods be used to supplement theoretical and experimental values found in current thermodynamic tables. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Vertical excitation energies for ribose and deoxyribose nucleosidesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2007Remmick So Abstract Vertical excitation energies for DNA and RNA nucleosides are determined with electron structure calculations using the time-dependent density functional theory (TDDFT) method at the B3LYP/6-311++G(d,p) level for nucleoside structures optimized at the same level of theory. The excitation energies and state assignments are verified using B3LYP/aug-cc-pVDZ level calculations. The nature of the first four excited states of the nucleosides are studied and compared with those of isolated bases. The lowest n,* and ,,* transitions in the nucleoside remain localized on the aromatic rings of the base moiety. New low-energy n,* and ,,* transitions are introduced in the nucleosides as a result of bonding to the ribose and deoxyribose molecules. The effect on the low-lying excited state transitions of the binding to phosphate groups at the 5,- and 3,,5,-hydroxyl sites of the uracil ribose nucleoside are also studied. Some implications of these calculations on the de-excitation dynamics of nucleic acids are discussed. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007. [source] A theoretical investigation of the excited states of OCLO radical, cation, and anion using the CASSCF/CASPT2 methodJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2007Zi-Zhang Wei Abstract Using the complete active space self-consistent field method with a large atomic natural orbital basis set, 10, 13, and 9 electronic states of the OClO radical, OClO+ cation, and OClO, anion were calculated, respectively. Taking the further correlation effects into account, the second-order perturbation (CASPT2) calculations were carried out for the energetic calibration. The photoelectron spectroscopy of the OClO radical and OClO, anion were extensively studied in the both case of the adiabatic and vertical ionization energies. The calculated results presented the relatively complete assignment of the photoelectron bands of the experiments for OClO and its anion. Furthermore, the Rydberg states of the OClO radical were investigated by using multiconfigurational CASPT2 (MS-CASPT2) theory under the basis set of large atomic natural orbital functions augmented with an adapted 1s1p1d Rydberg functions that have specially been built for this study. Sixteen Rydberg states were obtained and the results were consistent with the experimental results. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 467,477, 2007 [source]
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