FUNDAMENTALS AND TORSIONAL COMBINATION BANDS OF TWO ISOMERS OF THE OCS-CO$_{2}$ COMPLEX

Abstract

Infrared spectra of two isomers of the weakly bound OCS-CO$_{2}$ complex were observed using a tunable diode laser to probe a pulsed supersonic slit-jet. Spectra were recorded in the regions of OCS $\nu_{1}$ ($\sim$2060 cm$^{-1}$) and CO$_{2}$ $\nu_{3}$ ($\sim$2349 cm$^{-1}$) fundamental stretching vibrations. The lowest energy isomer (isomer \textit{a}) was previously studied by microwave spectroscopy. \textbf{88}, 687-690 (1988).} Here we report the first infrared observation of isomer \textit{a} and also detection of a new higher energy form (isomer \textit{b}). Structures were determined with the help of isotopic substitution. Both isomers are planar, with slipped near-parallel geometries. In isomer \textit{a}, the intermolecular (centre of mass) separation is 3.55 \AA\ and the C atom of the CO$_{2}$ is closer to the S atom of the OCS. In isomer \textit{b}, the C atom of CO$_{2}$ slides closer to the O atom of OCS and the center of mass separation increases to 3.99 \AA. \textbf{130}, 224310 (2009).} Three combination bands involving the intermolecular torsional (out-of-plane bend) vibrations were also analyzed. The out-of-plane torsional frequencies were measured to be 18.8 cm$^{-1}$ and 15.9 cm$^{-1}$ for isomers \textit{a} and \textit{b}, respectively, indicating that isomer \textit{a} is indeed more bound than isomer \textit{b}.