INFRARED SPECTRA OF He--CS$_2$, Ne--CS$_2$, AND Ar--CS$_2$

Abstract

Infrared spectra of weakly bound Rg--CS$_2$ (Rg = He, Ne, and Ar) clusters formed in a pulsed supersonic slit-jet expansion have been recorded by exciting the CS$_2$ $\nu_3$ fundamental band ($\sim$ 1535 cm$^{-1}$) using a tuneable diode laser. Spectra were well fitted to a conventional semi-rigid asymmetric rotor Hamiltonian. The He--CS$_2$ spectrum was assigned to an a-type band, while spectra of Ne--CS$_2$ and Ar--CS$_2$ were well described by b-type bands, indicating a/b axis switching in transition from the He--CS$_2$ complex to the Ne--CS$_2$ and Ar--CS$_2$ complexes. The results show that the complexes have vibrationally averged T-shaped structures. The determined structural parameters along with the observed vibrational shifts are $R=3.81, 3.57$ and $3.71$ {\AA}, $\theta = 80.0, 86.9$ and 86.4$^irc}$ and $\Delta\nu = 0.171, 0.181$ and $0.067$ cm$^{-1}$ for He--CS$_2$, Ne--CS$_2$ and Ar--CS$_2$, respectively. Here, $R$ is the distance between the rare gas and the carbon atom, $\theta$ is the the angle between $R$ and and the CS$_2$ axis and $\Delta\nu$ is the vibrational shift with respect to the free CS$_2$ monomer.