Frequency shifts on condensation

Dispersion Forces, Frequency Shifts on Condensation, and the VPIE... 

Table 5.4 Gas phase frequencies and frequency shifts on condensation, and anharmonicity constants for CHCI3 and CDCI3 in cm-1 (Jancso, G., Jakli, Gy. and Fetzer, C. Z., Naturforsch. 38a, 184 (1983)) ...

Table 5.6 Calculated and observed frequency shifts on condensation for CS2...

Molecules vibrate at fundamental frequencies that are usually in the mid-infrared. Some overtone and combination transitions occur at shorter wavelengths. Because infrared photons have enough energy to excite rotational motions also, the ir spectmm of a gas consists of rovibrational bands in which each vibrational transition is accompanied by numerous simultaneous rotational transitions. In condensed phases the rotational stmcture is suppressed, but the vibrational frequencies remain highly specific, and information on the molecular environment can often be deduced from hnewidths, frequency shifts, and additional spectral stmcture owing to phonon (thermal acoustic mode) and lattice effects. 

Most theoretical interpretations of condensed phase IE s have depended heavily on spectroscopic measurements of ZPE shifts to define limits on parameter assignments (force constant shifts). It is therefore a matter of some importance to determine the magnitude of dielectric corrections to be applied to such shifts. Fortunately dielectric corrections are larger than typical spectroscopic uncertainties in phase frequency shifts only for very intense IR bands, and therefore dielectric corrections are very often unnecessary. 

Thus, the effect of microviscosity in condensed media has an effect on frequency that can be comparable to or larger than the frequency shift caused by the addition of mass. This interference has the same origin as the frictional interference observed with the oscillating crystal in gas (4.15), except that it is much more severe in liquids. 

In contrast to the subsystem representation, the adiabatic basis depends on the environmental coordinates. As such, one obtains a physically intuitive description in terms of classical trajectories along Born-Oppenheimer surfaces. A variety of systems have been studied using QCL dynamics in this basis. These include the reaction rate and the kinetic isotope effect of proton transfer in a polar condensed phase solvent and a cluster [29-33], vibrational energy relaxation of a hydrogen bonded complex in a polar liquid [34], photodissociation of F2 [35], dynamical analysis of vibrational frequency shifts in a Xe fluid [36], and the spin-boson model [37,38], which is of particular importance as exact quantum results are available for comparison. 

The vibrational levels of a molecule in a condensed matter system are influenced by the surrounding medium through intermolecular interactions. The time-averaged forces exerted by the solvent on a molecular oscillator cause a static shift in the vibrational absorption frequency. The frequency shifts of the vibrational transitions of a molecule between the gas phase and a condensed matter environment is an indicator of the effect of the solvent on the internal mechanical degrees of freedom of a solute. 

There is a remarkable shielding effect, generally classified as ring current effect on the Li resonance in polyhapto lithium compounds of organic n-systems [57-66], where lithium is situated above the plane of the n-cloud (Table 4). Low-frequency and high-frequency shifts indicate diatropic and paratropic properties, respectively. The shielding effect is most pronounced for situations where Li" is sandwiched between two ic-systems [61, 62, 66], but smaller than expected in dianions of condensed benzenoid aromatics. 

Another intriguing point is that non-exponential damping of impurity motional states in a BEC provides an experimentally feasible example of manifestation of non-mean-field effects in a BEC. Up to now, only few experimental works on non-mean-field effects in BECs are available influence of a large thermal fraction of a bosonic system not far below the condensation point on damping and frequency shifts of elementary excitations was studied in Ref. [Jin... 

The above correlations relate only to spectra obtained in non-polar solvents, and departures from them are common when samples are examined in the solid or liquid state. Hartwell, Richards and Thompson [12] carried out a general study of the influence of physical state on a series of carbonyl compounds and found wide variations in the liquid state. Similarly, in the vapour phase the carbonyl frequencies were found to be appreciably different from those obtained in solution. Acetone, for example, absorbed at 1742 cm in the vapour phase, whereas in solution the frequency lay between 1728 cm and 1718 cm , depending on the solvent. Similarly, didecyl ketone absorbed at 1740 cm in the vapour state, and between 1724 cm and 1717 cm in solution. Dubois et al. [97] have recently given the vapour phase frequencies for a number of ketones, where the same effect is shown. It is probable that some form of dipolar association is occurring in the condensed phase [100,101], resulting in a low-frequency shift of the order of 20 cm". As far as possible, therefore, frequency measurements on ketones should be carried out in solution. 

It is known that optical bands of chromophores in condensed phase have a visible frequency shift as compared with the bands of the same chromophores in vapours [20]. This means that an interaction with other molecules influences the electronic subsystem of a chromophore. Therefore, the electronic wave functions and the distance between electronic levels of the chromophore depend on its environment. Hence the energy of the electronic exdtation of the chromophore is a function of the coordinates ft of the neighbouring molecules ... 

Surface Acoustic Waves (SA Ws). The basic idea of this technique is to use the dependence of the frequency and propagation of surface acoustic waves on mass loading in a film. The porous film has to be deposited on a piezoelectric substrate (quartz), which is then placed into a physisorption setup to condense nitrogen at 77 K. Adsorption and condensation of N2 result in a shift of the oscillation frequency, and thus measurements of the oscillation frequency as a function of N2 partial pressure provide an adsorption-desorption isotherm.30 Although the technique has proven to provide a concise characterization of porous films,29,30 the requirement for the deposition directly onto the SAW piezoelectric substrate represents a certain restriction. 

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