ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Raman scattering in liquid (and in some cases in solid) isotopic mixtures of HC1 and DC1 is analyzed to prove recent theories by Bratos and Tarjus [Phys. Rev. A 32, 2431 (1985)], Logan [Mol. Phys. 58, 97 (1986)], and Knapp [J. Chem. Phys. 81, 643 (1984)] on vibrational line broadening in liquids. The concentration and temperature dependencies of isotropic [Ji(ω)] and anisotropic [Ja(ω)] line shapes have been studied between triple point (Tt) and critical temperature (Tc). It has been found that in accordance with the Bratos–Tarjus theory, Ji (ω) is much more sensitive of isotopic composition of the liquid than Ja(ω). An analysis of the concentration dependence of the broadening parameters near Tt illustrates the importance of cross correlations between the environmental broadening and the resonant intermolecular coupling. The spectral activity of three-particle resonant transfer also becomes significant. From the change of the maximum of Ji(ω) with isotopic dilution, which is a linear function of mole fraction, the dipole moment derivative δμ/δq is estimated to be more than twice that of its gas phase value. The asymmetry of the isotropic bands of both HC1 and DC1 changes with concentration at constant temperature. With increasing temperature, Ji(ω) of pure and diluted samples narrows as T−0.5 and T−0.3, respectively. Ji(ω) has been found to be intermediate between the slow and the fast modulation limit. From the high frequency wing of Ji (ω) the time constant of the zeroth order memory function was obtained. Its activation energy increases with increasing T. This is in qualitative agreement with the temperature dependence of the Enskog collision time and the spin–rotational correlation time. Taking into account the results of the Bratos–Tarjus theory, orientational correlation times τ(2) are determined from Ja (ω). The Raman method yields τ(2) values which are twice as long as those determined from NMR relaxation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.457072
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