Infrared Spectroscopy of Symmetric and Spherical Top Molecules for Space Observation, Volume 2

2Interactions Between a Molecule and Its Solid Environment

Volumes 1 and 2 of this series [DAH 17, DAH 19a], describe the theoretical models developed for determining the absorption spectra of (homonuclear or heteronuclear) diatomic molecules and (linear or nonlinear, symmetric or non-symmetric) triatomic molecules trapped in nanocages of inert matrices of rare gases or clathrate hydrates at very low temperatures.

In rare gas matrices, the trapped molecule can occupy, depending on its size, composition and geometry, a simple substitution site (single substituted atom) or double substitution site (two substituted atoms). The distortion of the nanocage is determined by the iterative method, based on the Green functions of the perfect crystal. In clathrate hydrates, the molecule can occupy a small cage and/or a large cage in structure I or II.

In this volume, the theoretical models developed in Volumes 1 and 2 are applied to the NH₃ symmetric and/or CH₄ spherical tops trapped in a nanocage of rare gas matrix, clathrate, fullerene or adsorbed on a graphite substrate.

The perturbed motions of the molecule are studied using an atom–atom potential for describing the interaction between the trapped molecule and its environment. The frequency shift and the line broadening are determined by the Liouville formalism and using the cumulant expansion techniques of the evolution operator of the optically active system in a solid or liquid constrained environment known as a heat bath.

2.1. ...