Infrared Study of Liquids. I. The Theory of the ir Spectra of Diatomic Molecules in Inert Solutions

Abstract

A theory is proposed to explain the ir spectra of inert solutions of diatomic molecules. The theory is a stochastic-type theory related to similar theories of the NMR spectra. The vapor-solution band shifts are shown to depend on the difference between the solvent–solute interaction energies of the two vibrational states involved in the transition. The band profiles are basically asymmetrical; nevertheless, symmetric limiting forms exist as well. The theory predicts the existence of a continuous sequence of band forms comprising, among others, the profile with P- and R-type wings, the Lorentzian profile, the Gaussian profile, the Voigt profile, and several sorts of asymmetric profiles. The relation between a given band form and the nature of the dominating relaxation process is discussed.

Shape of the carbon monoxide infrared absorption band of carboxyheme proteins as a probe of the protein anharmonicity

“…Contribution of different interactions into shape of a vibrational band was studied in a number of publications [1,4,5,11,12,22,24,29,34]. First, resonant transfer of vibrational energy between identical molecules causes exciton-like broadening of the band.…”

Models of picosecond-scale mobilities in glassy and polycrystalline quinoline

“…Second, these particular models rest on rather specific boundary conditions (15) such as form of intermolecular potential and dimensionality of the lattice, a situation which has been criticized (18) (it appears rightly) as going against the universal experimental applicability of eq. [8] as well as its worthiness at "shorter t". Third, eq.…”

“…Third, eq. [8] can also result from a model of many, parallel and independent relaxation pathways, each of which is governed by pure exponential decay,…”

“…However, it is difficult to be confident in singling out one of the fundamental physical processes that have been shown to lead to a relaxation function of the type of eq. [8] (15) such as defect diffusion or hierarchically-constrained dynamics. First, it seems that these physical models are only valid for long t, a situation that is not satisfied by Can.…”

“…The most convenient approach then resolves, to all practical purposes, to a judicious and problem-related choice of the autocorrelation function of the fluctuation AV(t) of the intermolecular potential V(t) at the oscillator displacement coordinate (3,(5)(6)(7). In turn, AV(t) is considered to be proportional to Hl(t) and, hence, to the shift of the stochastic transition frequency fi-'Hl(t) = wl(t) (counted from the band center, o,, ol = w -o,) (8). Consequently, the problem of having to write out the physical model of the particular form of the amplitude autocorrelation is then reduced to that of formulating a relevant and physically sound correlation function ("modulation function") of o ,(t) (2),…”