%0 Journal Article
%T A Simulation Study of the Far-Infrared Absorption Spectra of HCl Diluted in Liquid Ar
%A A. Padilla
%A J. P¨Śrez
%J International Journal of Spectroscopy
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/485432
%X The far-infrared absorption coefficient of HCl diluted in liquid Ar has been calculated by using a mixed classical-quantum stochastic simulation approach. The simulated spectra have been compared with the available experimental data at different thermodynamic conditions without using ad hoc fitting parameters. Despite the fact that some discrepancies can be observed in the high frequency side of the far-infrared bands, a reasonable agreement has been found between the theoretical and the experimental spectral profiles. Both, classical and quantum simulated line shapes were comparatively analyzed, determining the time scales involved in the rotational spectra. 1. Introduction Infrared (IR) spectroscopy has been a useful tool in chemistry and physics to study and characterize a large variety of molecular systems. Because it is a nondestructive method, it is useful to study the structure of complex systems such as biological molecules, proteins, DNA, and membranes [1, 2]. In the last decade, IR spectroscopy has been used in the study of healthy and nonhealthy human tissues [2], and as well it has been employed in the industry field for quality control. On the other hand, IR spectroscopy has been highly successful in measuring the degree of polymerization in polymer manufacture [1, 2] and also has a forensic purpose, being used in the analyze of substances, such as alcohol, drugs, fibers, blood, and paints [2, 3]. Far-infrared spectroscopy is closely related to the rotational dynamics of a wide range of molecular systems. In particular, the study of far-infrared absorption spectra of diatomic polar molecules diluted in inert solvents gives relevant information about intermolecular interactions and the dynamical properties of the solvent variables involved in the diatomic relaxation [4, 5]. The rotational diatomic relaxation in dense fluids determines the basic properties of the far-infrared absorption bands, which, depending on the diatomic molecule and the thermodynamic conditions of the solution, can present a fine rotational structure associated with the R-branch of the gas phase spectra. In that case, as it happens with the HCl immerse in dense Ar [6], a quantum model for the diatomic rotation is necessary in order to explain the spectral properties of the far-infrared bands. In a recent work [6], we have developed a mixed classical-quantum stochastic simulation (MCQSS) for the rotational and translational degrees of freedoms of both the solute HCl molecule and the Ar solvent atoms. In this study, the diatomic was treated as a quantum rotor which is
%U http://www.hindawi.com/journals/ijs/2013/485432/