Vibrational frequency shift solvent induced

More recently, the PCM has been amply extended to the treatment of vibrational spectroscopies, by taking into account not only solvent-induced vibrational frequency shifts, but also vibrational intensities in a unified and coherent formulation. Thus, models to treat IR [8], Raman [9], IR linear dichroism [10], VCD [11] and VROA [12] have been proposed and tested, by including in the formulation local field effects, as well as an incomplete solute-solvent regime (nonequilibrium) and, when necessary, by extending the model to the treatment of specific solute-solvent (or solute-solute) effects. 

The instantaneous OH frequency was calculated at each time step in an adiabatic approximation (fast quantal vibration in a slow classical bath ). We applied second-order perturbation theory, in which the instantaneous solvent-induced frequency shift from the gas-phase value is obtained from the solute-solvent forces and their derivatives acting on a rigid OH bond. This method is both numerically advantageous and allows exploration of sources of various solvent contributions to the frequency shift. 

Equations 1-5 completely define the "hard fluid" model for solvent induced changes in the vibrational frequency of a diatomic (or pseudo-diatomic) solute. The only adjustable parameter in this model is the coefficient Ca appearing in equation 5. The other parameters, such as the diameters of the solute and solvent as well as the solvent density and temperature, are determined using independent measurements and/or parameter correlations (37). The value of Ca can be determined with a minimal amount of experimental data. In particular we use the frequency shift observed in going from the dilute gas to a dense fluid to fix the value of Ca. Having done this, the... 

FT i.r, spectroscopy has been used to determine the solvent-induced frequency shifts for the C—H stretching bands of n-octane. Measurement of the FT i.r. spectra for HCl and DCl over the range 2840—8450cm and for HI and DI over the range 3000—10 380 cm" allowed accurate prediction of the TCI and TI spectra. For D2 0, the high resolution (5 x 10 cm ) available using FT i.r. spectroscopy enabled an extended and more precise set of rotational levels to be derived for the vibrational states (000), (020), (100), and (001). Rotational constants and vibrational term values were evaluated for from FT i.r. 

For vibrational properties, solute—solvent short-range interactions not only can induce a shift in the frequency but they can also modify the normal modes. This effect can be taken into account only by including some specific solvent molecules within the QM portion of the system. This supermolec-ular approach, however, introduces some additional aspects that make the analysis more complex. First of aU, the selection of the number and the position of the solvent molecules to be included in the QM part is not unequivocal moreover, as now the solvent enters as a QM component, we cannot easily dissect the response of the solute from that of the solvent molecules. 

The complexation-induced frequency shifts for ArnDF/HF allow the characterization of the small shifts in monomer vibrational energy upon the incremental addition of solvent atoms. For large values of n, the... 

We have presented experimental and theoretical results for vibrational relaxation of a solute, W(CO)6, in several different polyatomic supercritical solvents (ethane, carbon dioxide, and fluoroform), in argon, and in the collisionless gas phase. The gas phase dynamics reveal an intramolecular vibrational relaxation/redistribution lifetime of 1.28 0.1 ns, as well as the presence of faster (140 ps) and slower (>100 ns) components. The slower component is attributed to a heating-induced spectral shift of the CO stretch. The fast component results from the time evolution of the superposition state created by thermally populated low-frequency vibrational modes. The slow and fast components are strictly gas phase phenomena, and both disappear upon addition of sufficiently high pressures of argon. The vibrational... 

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