Time-resolved vibrational spectroscopy

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Time-resolved vibrational spectroscopy     

Low-frequency vibrational modes of glutamine

High-resolution terahertz absorption and Raman spectra of glutamine in the frequency region 0.2 THz-2.8 THz are obtained by using THz time domain spectroscopy and low-frequency Raman spectroscopy. Based on the experimental and the computational results, the vibration modes corresponding to the terahertz absorption and Raman scatting peaks are assigned and further verified by the theoretical calculations. Spectral investigation of the periodic structure of glutamine based on the sophisticated hybrid density functional B3LYP indicates that the vibrational modes come mainly from the inter-molecular hydrogen bond in this frequency region.     

Lattice vibrational analysis of polyacene

Within an extended Su-Schrieffer-Heeger model, we made a lattice vibrational analysis of polyacene. In a singly-charged polyacene, the ground state contains an interchain-coupled polaron of quasi-D2h symmetry, around which we found thirteen localized modes in total. Among these localized modes, five (three B2u and two B3u) are infrared active, six (four Ag and two B1g) modes are Raman active, and the other two localized modes are asymmetric, which are both infrared active and Raman active. For the case a charged polaron is coupled with a neutral soliton in a finite polyacene chain, the vibrational modes are also calculated to display the coupling effect between self-trapping excitations on phonons. It is found that the localized phonons are determined mainly by the charged polaron, but the number and frequencies of the localized modes are influenced by the existence of the neutral soliton.     

Lattice vibrational spectrum of diamond

The lattic dynamics of covalent crystals are discussed with reference to known models. The dispersion curves of diamond have been computed on the basis of the shell model of Cochran applicable to covalent crystals. Parameters have been determined using elastic constants and dispersion curves along the Δ and A directions from the neutron spectrometric data of Warren et al. In general there is good agreement between the calculated curves and experiment. The average error is about 4.8%. Although the calculated curves seem to be a definite improvement over the curves calculated by Smith there appears to be a certain discrepancy between theory and experiment. Plausible causes of this discrepancy are pointed out.     

Lattice vibrational properties of TmTe

We have investigated the lattice dynamical properties of a TmTe compound by using a breathing shell model suitable for this compound. The calculated phonon dispersion curves (PDC) reveal that this compound does not show any anomaly in their phonon properties. Our results on PDC, phonon density of states and lattice specific heat reveal that the phonon properties of this compound are like the other rare earth chalcogenides, particularly Eu-chalcogenides. We emphasize the need of measurements of the complete PDC of TmTe to support the present results on the calculated phonon properties.     

The vibrational spectra of dibenzofuran

Infrared spectra, polarized along all three orthogonal crystal axes of dibenzofuran, have been recorded from 50 to 3500 cm^?1. The polarized Raman spectra of single crystals have been measured in all possible crystal orientations, and this information has been supplemented by the measurement of depolarization ratios of the Raman lines in solution and melt spectra. This work extends the range of an earlier study carried out before the crystal structure of dibenzofuran was known. With the new data, several changes in the assignment of the molecular fundamentals are necessary; even so, the experimental assignments remain incomplete in many instances. Some lattice modes of the single crystal were observed in the infrared and Raman spectra, and a partial assignment is presented.     

A vibrational analysis of trichloroiodomethane

The infrared and Raman spectra of CCl₃I have been recorded. Band assignments have been made on the basis of the infrared results, and the Raman spectrum has been interpreted in terms of the fundamentals of CCl₃I, with additional bands being assigned to decomposition products of CCl₃I. A Urey-Bradley force constant calculation has been made, transferring results from the earlier work of Ngai and Mann.     

The vibrational levels of C2H2 using an internal coordinate vibrational hamiltonian

A vibrational (J = 0) hamiltonian has been derived using the method of Sutcliffe, for tetra-atomic molecules, in terms of three bond lengths and three bond angles. An analysis of the angle dependent parts of this hamiltonian is given. Suitable expansion functions for vibrational calculations with this hamiltonian are discussed. An application to find the low lying vibrational levels of C₂H₂ using the potential surface of Halonen et al. is described.     

The vibrational Zeeman effect

The theory of the vibrational Zeeman effect in symmetric top molecules is presented. It is shown that vibrational g factors may be related to rotational g factors and estimates are made of their magnitude for a number of molecules; these calculations indicate that vibrational Zeeman effects should be observable in symmetric top molecules in degenerate vibrational states. In addition, the novel features of the theory for linear molecules are discussed.     

Nonlinear interferometric vibrational imaging

Coherent anti-Stokes Raman scattering (CARS) processes are "coherent," but the phase of the anti-Stokes radiation is lost by most incoherent spectroscopic CARS measurements. We propose a Raman microscopy imaging method called nonlinear interferometric vibrational imaging, which measures Raman spectra by obtaining the temporal anti-Stokes signal through nonlinear interferometry. With a more complete knowledge of the anti-Stokes signal, we show through simulations that a high-resolution Raman spectrum can be obtained of a molecule in a single pulse using broad band radiation. This could be useful for identifying the three-dimensional spatial distribution of molecular species in tissue.     

The vibrational spectrum of fluorobenzene

The high resolution infrared spectra of three fluorobenzene isotopes were obtained and interpreted. Vibrational assignments of most bands were made and values for most of the fundamental vibrations were obtained. Accurate values for the infrared inactive a₂ vibrations were also obtained. Several major modifications of literature values for the fundamentals were made and a Fermi resonance interaction identified.     

Theoretical prediction of vibrational spectra: The out-of-plane force field and vibrational spectra of pyridine

The harmonic force field for the out-of-plane vibrations of pyridine has been calculated from ab initio Hartree-Fock wavefunctions obtained with a 4–21 basis set of contracted Gaussians. To account for systematic errors, the calculated force constants were scaled, using only two independent sclae factors which were transferred unchanged from benzene. The resulting scaled quantum mechanical force field, which is strictly a priori in that it is not based on any experimental data on pyridine, predicts the 64 out-of-plane fundamental frequencies of pyridine and its deuterated isotopomers of C_2v symmetry with a mean deviation from experiment of only 8.5 cm^?1. Addition of polarization functions to the basis set for the nitrogen atom and refinement of the two scale factors by fitting them to the observed pyridine spectra produce no significant improvement in the fit. Assignments of the vibrational spectra are discussed.     

Intramolecular vibrational redistribution and vibrational predissociation in 9-cyanoanthracene-Ar van der waals complexes

Processes of intramolecular vibrational redistribution and vibrational predissociation in 9-cyanoanthracene—Ar van der Waals complexes are investigated; their effect on the probabilities of nonradiative transitions is establsihed. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 184–191, March–April, 1998.