A two-dimensional model for the infrared and microwave spectrum of diatomic molecules trapped in monatomic crystals

Abstract

A two-dimensional model is developed to approach the spectral properties of a diatomic polar molecule embedded in a monatomic crystal. This model introduces two rotational degrees of freedom in the limit of small amplitude oscillations. The first one describes the angular (planar) motion of the dipole moment of the molecule. The second one is connected to some collective motion of the nearest atom neighbors of this molecule (called the first shell). The remaining atoms of the crystal act as a thermal bath. This problem is treated first in a classical and then in a quantum version. The experimental data presently available (i.e., for CO molecules trapped in argon crystal) are compared to the theoretical results.

The libron–phonon coupling and the IR absorption spectra of diatomic molecules in a simple liquid

“…In the coordinate system fixed in the molecule the dipole moment components are (9) with lL(r) = J.to + ILIAr and re being the equilibrium intermolecular distance. As we have assumed that the Az displacements are mainly Ar, the z component of the dipole moment is just lL(r).…”

“…This approach allows them to obtain the IR spectrum of HCI in liquid CC4 after fitting various parameters. More recently, Mauricio et al 9 again used the idea of molecules in cages. This is a 2D dynamical model in which the cage interacts with a viscous isothermal bath through an indirect coupling between the librational motion of the molecule and phonons.…”