Home About us Contact
|
Home About us Contact | ||
|
|
||
Vibrational States (vibrational + states)
Selected AbstractsSymmetric Stretching Vibration of CH4 in Clathrate Hydrate StructuresCHEMPHYSCHEM, Issue 14 2010Dr. Hiroshi Ohno Movers and shakers: Vibrational states of CH4 molecules encaged in three clathrate hydrate structures are studied (see picture). Guest methane distribution in the structure-H 512 and 435663 host cavities is revealed for the first time. Raman profiles of the CH4 vibration are dependent not only on types of water cages, but also on clathrate structures (guest compositions), suggesting distinctive differences in molecular interactions between the three hydrate systems. [source] Theoretical investigations on analytical potential energy function and spectroscopic parameters for the state b3,u of dimer 7Li2INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2007De-Heng Shi Abstract The SAC-CI (symmetry-adapted-cluster configuration-interaction) method presented in Gaussian 03 program package is applied to investigate the adiabatic potential energy curves (PECs) of 7Li2(b3,u). These calculations are performed at numbers of basis sets, such as 6-311++G(3df,3pd), 6-311++G(2df,2pd), 6-311++G(df,pd), D95V++, D95(3df,3pd), D95(d,p), cc-PVTZ, 6-311++G and 6-311++G(d,p). All the ab initio calculated points are fitted to the analytic Murrell-Sorbie functions and then used to compute the spectroscopic parameters. The analytic potential energy function (APEF) for this b3,u state is reported. By comparison, the spectroscopic parameters reproduced by the APEF attained at 6-311++G(2df,2pd) are found to be very close to the latest experimental findings. With the APEF obtained at the SAC-CI/6-311++G(2df,2pd) level of theory, a total of 62 vibrational states is found when J = 0. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants for these vibrational states are also reported. The reasonable dissociation limit for this state is deduced using the calculated results at present. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Rotational CARS thermometry at high temperature (1800 K) and high pressure (0.1,1.55 MPa)JOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2007F. Vestin Abstract Dual-broadband rotational CARS (DB-RCARS) thermometry has been investigated at high temperature and high pressure. Single-shot measurements were performed at 1800 K, in air and nitrogen at pressures up to 1.55 MPa and in oxygen at pressures up to 0.5 MPa. For all conditions, the resonant signal contribution to the spectra clearly dominated over the non-resonant one, implying the high potential for DB-RCARS for temperature and concentration measurements also at the high temperatures and pressures used in the present investigation. The relative standard deviation was generally ,2% for single-shot data at pressures from 0.5 to 1.55 MPa. At the investigated temperature, 1800 K, rotational lines from thermally excited vibrational states could be observed in the highly resolved experimental spectra. Using a previously developed weighting procedure applied to these lines, it was demonstrated that the temperature standard deviation could be lowered with as much as 30%. Copyright © 2007 John Wiley & Sons, Ltd. [source] Degenerate and two-color resonant four-wave mixing applied to the rotational characterization of high-lying vibrational states of formaldehyde (Ã, 1A2),JOURNAL OF RAMAN SPECTROSCOPY, Issue 1-3 2006M. Tulej Abstract Degenerate and two-color resonant four-wave mixing techniques (DFWM and TC-RFWM) are applied to determine rotational constants of high-lying vibrational levels in the first excited singlet state Ã(1A2) of formaldehyde. It has been demonstrated that the sensitivity of the spectroscopic technique is applicable to the low-density environment of a supersonic molecular beam and to predissociating transitions displaying low fluorescence quantum yield. In addition, we take advantage of the superior selectivity of the double-resonance method, TC-RFWM, to isolate and assign transitions in the congested region of the (one-color) DFWM spectra. The line positions of 25 well-isolated transitions are determined in the band and yield the rotational constants A, B, C and the origin ,e. The accuracy of the constants is determined by performing the same procedure for the band where literature data is available for comparison. Copyright © 2006 John Wiley & Sons, Ltd. [source] On the Einstein model for EXAFS parallel and perpendicular mean-square relative displacementsJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2008A. Sanson The correlated Einstein model for EXAFS parallel and perpendicular mean-square relative displacements (MSRDs) is discussed. By means of dynamical simulations on different crystalline structures, the error owing to the Einstein-fit model on the EXAFS MSRDs is estimated as a function of the standard deviation of the density of vibrational states. This error should be taken into account to improve the accuracy of the MSRDs. [source] Activation of large lons in FT-ICR mass spectrometryMASS SPECTROMETRY REVIEWS, Issue 2 2005Julia Laskin Abstract The advent of soft ionization techniques, notably electrospray and laser desorption ionization methods, has enabled the extension of mass spectrometric methods to large molecules and molecular complexes. This both greatly extends the applications of mass spectrometry and makes the activation and dissociation of complex ions an integral part of these applications. This review emphasizes the most promising methods for activation and dissociation of complex ions and presents this discussion in the context of general knowledge of reaction kinetics and dynamics largely established for small ions. We then introduce the characteristic differences associated with the higher number of internal degrees of freedom and high density of states associated with molecular complexity. This is reflected primarily in the kinetics of unimolecular dissociation of complex ions, particularly their slow decay and the higher energy content required to induce decomposition,the kinetic shift (KS). The longer trapping time of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) significantly reduces the KS, which presents several advantages over other methods for the investigation of dissociation of complex molecules. After discussing general principles of reaction dynamics related to collisional activation of ions, we describe conventional ways to achieve single- and multiple-collision activation in FT-ICR MS. Sustained off-resonance irradiation (SORI),the simplest and most robust means of introducing the multiple collision activation process,is discussed in greatest detail. Details of implementation of this technique, required control of experimental parameters, limitations, and examples of very successful application of SORI-CID are described. The advantages of high mass resolving power and the ability to carry out several stages of mass selection and activation intrinsic to FT-ICR MS are demonstrated in several examples. Photodissociation of ions from small molecules can be effected using IR or UV/vis lasers and generally requires tuning lasers to specific wavelengths and/or utilizing high flux, multiphoton excitation to match energy levels in the ion. Photodissociation of complex ions is much easier to accomplish from the basic physics perspective. The quasi-continuum of vibrational states at room temperature makes it very easy to pump relatively large amounts of energy into complex ions and infrared multiphoton dissociation (IRMPD) is a powerful technique for characterizing large ions, particularly biologically relevant molecules. Since both SORI-CID and IRMPD are slow activation methods they have many common characteristics. They are also distinctly different because SORI-CID is intrinsically selective (only ions that have a cyclotron frequency close to the frequency of the excitation field are excited), whereas IRMPD is not (all ions that reside on the optical path of the laser are excited). There are advantages and disadvantages to each technique and in many applications they complement each other. In contrast with these slow activation methods, the less widely appreciated activation method of surface induced dissociation (SID) appears to offer unique advantages because excitation in SID occurs on a sub-picosecond time scale, instantaneously relative to the observation time of any mass spectrometer. Internal energy deposition is quite efficient and readily adjusted by altering the kinetic energy of the impacting ion. The shattering transition,instantaneous decomposition of the ion on the surface,observed at high collision energies enables access to dissociation channels that are not accessible using SORI-CID or IRMPD. Finally, we discuss some approaches for tailoring the surface to achieve particular aims in SID. © 2004 Wiley Periodicals, Inc., Mass Spec Rev 24:135,167, 2005 [source] Localized dynamics in network glassesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004C. Halcoussis Abstract In this work we studied by means of inelastic x-ray scattering (IXS) the nature of collective excitations in the network forming glass Ba(PO3)2. In particular, we provide the first experimental evidence for the presence of a multitude of collective excitations in a glass, situated in the energy span from 5 to 20 meV. Their nearly dispersionless evolution from 5 to 25 nm,1 suggests their largely localized nature mainly caused by the incorporated metallic cations acting as network modifiers. We suggest that these non-propagating vibrational states result from an eigenvector exchange with propagating density fluctuations of an "acoustic" character. This study gives an insight into the excess of vibrational states known as the "Boson" peak from many neutron and optical scattering experiments and being omnipresent in all kinds of glasses. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Radio frequency magnetic field effects on molecular dynamics and iron uptake in cage proteinsBIOELECTROMAGNETICS, Issue 4 2010Oscar Céspedes Abstract The protein ferritin has a natural ferrihydrite nanoparticle that is superparamagnetic at room temperature. For native horse spleen ferritin, we measure the low field magnetic susceptibility of the nanoparticle as 2.2,×,10,6,m3,kg,1 and its Néel relaxation time at about 10,10,s. Superparamagnetic nanoparticles increase their internal energy when exposed to radio frequency magnetic fields due to the lag between magnetization and applied field. The energy is dissipated to the surrounding peptidic cage, altering the molecular dynamics and functioning of the protein. This leads to an increased population of low energy vibrational states under a magnetic field of 30,µT at 1,MHz, as measured via Raman spectroscopy. After 2,h of exposure, the proteins have a reduced iron intake rate of about 20%. Our results open a new path for the study of non-thermal bioeffects of radio frequency magnetic fields at the molecular scale. Bioelectromagnetics 31:311,317, 2010. © 2010 Wiley-Liss, Inc. [source] | ||||||||||