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Vertical Detachment Energy (vertical + detachment_energy)
Selected AbstractsA combined ab initio and Franck-Condon factor simulation study on the photodetachment spectrum of ScO2,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2009Edmond P. F. Lee Abstract Restricted-spin coupled-cluster single-double plus perturbative triple excitation {RCCSD(T)} potential energy functions (PEFs) of the 2B2 state of ScO2 and the 1A1 state of ScO2, were computed, employing the augmented correlation-consistent polarized-weighted core-valence quadruple-zeta (aug-cc-pwCVQZ) basis set for Sc and augmented correlation-consistent polarized valence quadruple-zeta (aug-cc-pVQZ) basis set for O, and with the outer core Sc 3s23p6 electrons being explicitly correlated. Franck-Condon factors, which include allowance for Duschinsky rotation and anharmonicity, were calculated using the computed RCCSD(T) PEFs, and were used to simulate the first photodetachment band of ScO2,. The simulated spectrum matches well with the corresponding experimental 355 nm photodetachment spectrum of Wu and Wang, J Phys Chem A 1998, 102, 9129, confirming the assignment of the photodetachment spectrum and the reliability of the RCCSD(T) PEFs used. Further calculations on low-lying electronic states of ScO2 gave adiabatic relative electronic energies (Te's) of, and vertical excitation energies (Tv's) to, the 2A1, 2B1, and 2A2 states of ScO2 (from the 2B2 state of ScO2), as well as electron affinities (EAs) and vertical detachment energies (VDEs) to these neutral states from the 1A1 state of ScO2,. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Transition metal sulfide clusters below the cluster,platelet transition: Theory and experimentPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2010Sibylle Gemming Abstract The structural and electronic properties of neutral and anionic molybdenum sulfide clusters with the composition Mo3Sn (n,=,0,12) were studied by density-functional calculations. The theoretical results are confirmed by a comparison with photoelectron spectra of the corresponding W3S anions providing experimental values for the vertical detachment energies (VDEs) and the highest occupied (HOMO) and lowest unoccupied (LUMO) gaps. For sulfur contents up to n,=,9 the clusters are composed of a central Mo3 unit, which is decorated by bridging, terminal, and three-fold coordinated S atoms. For n,>,9, a cleavage of the Mo3 center is observed. The formation of disulfide like ions is found for Mo3S9 and larger species. In accordance with investigations of MoSn, Mo2Sn, and Mo4Sn clusters, the heat of formation and the VDE reaches a maximum in the sulfur-rich region beyond the composition Mo:S,=,1:2. [source] Low-Energy-Barrier Proton Transfer Induced by Electron Attachment to the Guanine,,,Cytosine Base PairCHEMPHYSCHEM, Issue 4 2010Anna Szyperska Abstract The photoelectron spectrum of the anion of the guanine,,,cytosine base apair (GC)., is recorded for the first time. The observed variation in the spectral peak-height ratios with the source conditions suggests the presence of two or more anionic isomers. Two maxima of the broad bands in the photoelectron spectrum were measured at about 1.9 and about 2.6 eV. These values are very well reproduced by the vertical detachment energies of the B3LYP/6-31++G(d,p) calculated low-energy anionic structures, which are 1) the Watson,Crick base-pair anion with proton transferred from N1 of guanine to N3 of cytosine, 2) its analogue in which the proton is transferred from N9 of guanine to N7 of guanine, and 3) the global minimum geometry, which is formed from the latter anion by rotation of guanine about the axis approximately defined by C2 of guanine and C4 of cytosine. Furthermore, a minor difference in the stabilities of the two lowest energy anions explains the experimentally observed source (temperature) dependence of the PES spectrum. A rational procedure, based on the chemistry involved in the formation of anionic dimers, which enables the low-energy anions populated in the photoelectron spectrum to be identified is proposed. In contrast to the alternative combinatorial approach, which in the studied case would lead to carrying out quantum chemical calculations for 2000,2500 structures, the procedure described here reduces the computational problem to only 15 geometries. [source] The arsenic clusters Asn (n = 1,5) and their anions: Structures, thermochemistry, and electron affinitiesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2004Yi Zhao Abstract The molecular structures, electron affinities, and dissociation energies of the Asn/As (n = 1,5) species have been examined using six density functional theory (DFT) methods. The basis set used in this work is of double-, plus polarization quality with additional diffuse s - and p -type functions, denoted DZP++. These methods have been carefully calibrated (Chem Rev 2002, 102, 231) for the prediction of electron affinities. The geometries are fully optimized with each DFT method independently. Three different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The first dissociation energies De(Asn,1 -As) for the neutral Asn species, as well as those De(As -As) and De (Asn,1 -As,) for the anionic As species, have also been reported. The most reliable adiabatic electron affinities, obtained at the DZP++ BLYP level of theory, are 0.90 (As), 0.74 (As2), 1.30 (As3), 0.49 (As4), and 3.03 eV (As5), respectively. These EAad values for As, As2, and As4 are in good agreement with experiment (average absolute error 0.09 eV), but that for As3 is a bit smaller than the experimental value (1.45 ± 0.03 eV). The first dissociation energies for the neutral arsenic clusters predicted by the B3LYP method are 3.93 eV (As2), 2.04 eV (As3), 3.88 eV (As4), and 1.49 eV (As5). Compared with the available experimental dissociation energies for the neutral clusters, the theoretical predictions are excellent. Two dissociation limits are possible for the arsenic cluster anions. The atomic arsenic results are 3.91 eV (As , As, + As), 2.46 eV (As , As + As), 3.14 eV (As , As + As), and 4.01 eV (As , As + As). For dissociation to neutral arsenic clusters, the predicted dissociation energies are 2.43 eV (As , As2 + As,), 3.53 eV (As , As3 + As,), and 3.67 eV (As , As4 + As,). For the vibrational frequencies of the Asn series, the BP86 and B3LYP methods produce good results compared with the limited experiments, so the other predictions with these methods should be reliable. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 907,920, 2004 [source] Molecules for materials: Germanium hydride neutrals and anions.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2002Ge2Hn/Ge2H (n = 0, Molecular structures, electron affinities, thermochemistry of GeHn/GeH (n = 0 Abstract The GeHn (n = 0,4) and Ge2Hn (n = 0,6) systems have been studied systematically by five different density functional methods. The basis sets employed are of double-, plus polarization quality with additional s- and p-type diffuse functions, labeled DZP++. For each compound plausible energetically low-lying structures were optimized. The methods used have been calibrated against a comprehensive tabulation of experimental electron affinities (Chemical Reviews 102, 231, 2002). The geometries predicted in this work include yet unknown anionic species, such as Ge2H,, Ge2H, Ge2H, Ge2H, and Ge2H. In general, the BHLYP method predicts the geometries closest to the few available experimental structures. A number of structures rather different from the analogous well-characterized hydrocarbon radicals and anions are predicted. For example, a vinylidene-like GeGeH structure is the global minimum of Ge2H. For neutral Ge2H4, a methylcarbene-like HGë-GeH3 is neally degenerate with the trans -bent H2GeGeH2 structure. For the Ge2H anion, the methylcarbene-like system is the global minimum. The three different neutral-anion energy differences reported in this research are: the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). For this family of molecules the B3LYP method appears to predict the most reliable electron affinities. The adiabatic electron affinities after the ZPVE correction are predicted to be 2.02 (Ge2), 2.05 (Ge2H), 1.25 (Ge2H2), 2.09 (Ge2H3), 1.71 (Ge2H4), 2.17 (Ge2H5), and ,0.02 (Ge2H6) eV. We also reported the dissociation energies for the GeHn (n = 1,4) and Ge2Hn (n = 1,6) systems, as well as those for their anionic counterparts. Our theoretical predictions provide strong motivation for the further experimental study of these important germanium hydrides. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 1642,1655, 2002 [source] Comprehensive Analysis of DNA Strand Breaks at the Guanosine Site Induced by Low-Energy Electron AttachmentCHEMPHYSCHEM, Issue 1 2010Jiande Gu Prof. Dr. Abstract To elucidate the role of guanosine in DNA strand breaks caused by low-energy electrons (LEEs), theoretical investigations of the LEE attachment-induced CO ,-bonds and N-glycosidic bond breaking of 2,-deoxyguanosine-3,,5,-diphosphate (3,,5,-dGMP) were performed using the B3LYP/DZP++ approach. The results reveal possible reaction pathways in the gas phase and in aqueous solutions. In the gas phase LEEs could attach to the phosphate group adjacent to the guanosine to form a radical anion. However, the small vertical detachment energy (VDE) of the radical anion of guanosine 3,,5,-diphosphate in the gas phase excludes either CO bond cleavage or N-glycosidic bond breaking. In the presence of the polarizable surroundings, the solvent effects dramatically increase the electron affinities of the 3,,5,-dGDP and the VDE of 3,,5,-dGDP,. Furthermore, the solvent,solute interactions greatly reduce the activation barriers of the CO bond cleavage to 1.06,3.56 kcal,mol,1. These low-energy barriers ensure that either C5,O5, or C3,O3, bond rupture takes place at the guanosine site in DNA single strands. On the other hand, the comparatively high energy barrier of the N-glycosidic bond rupture implies that this reaction pathway is inferior to CO bond cleavage. Qualitative agreement was found between the theoretical sequence of the bond breaking reaction pathways in the PCM model and the ratio for the corresponding bond breaks observed in the experiment of LEE-induced damage in oligonucleotide tetramer CGTA. This concord suggests that the influence of the surroundings in the thin solid film on the LEE-induced DNA damage resembles that of the solvent. [source] Ionization-Induced Proton Transfer in Model DNA Base Pairs: A Theoretical Study of the Radical Ions of the 7-Azaindole DimerCHEMPHYSCHEM, Issue 12 2004Hsing-Yin Chen Dr. Abstract Proton-transfer reactions of the radical anion and cation of the 7-Azaindole (7AI) dimer were investigated by means of density functional theory (DFT). The calculated results for the dimer anion and cation were very similar. Three equilibrium structures, which correspond to the non-proton-transferred (normal), the single-proton-transferred (SPT) and the double-proton-transferred (tautomeric) forms, were found. The transition states for proton-transfer reactions were also located. The calculations showed that the first proton-transfer reaction (normal,SPT) is exothermic and almost barrier-free; therefore, it should occur spontaneously in the period of a vibration. In contrast, the second proton-transfer reaction (SPT,tautomer) was found to be far less-probable in terms of reaction energy and barrier. Hence, it was concluded that both (7AI)2and (7AI)2exist in the SPT form. The conclusion was further confirmed by the calculated electron vertical detachment energy (VDE) of the SPT form of (7AI)2, 1.33 eV, which is very close to the experimental measurement of 1.35 eV. The calculated VDEs of the normal and tautomeric (7AI)2forms were too small compared to the experimental value. The proton transfer process was found to be multidimensional in nature involving not only proton motion but also intermolecular rocking motion. In addition, IR spectra were calculated and reported. The spectra of the three structures showed very different features and, therefore, can be considered as fingerprints for future experimental identifications. The implications of these results to biology and spectroscopy are also briefly discussed. [source] | ||||||||||