15min:

J. NOROOZ OLIAEE, M. DEHGHANY, F. MIVEHVAR, MAHIN AFSHARI, N. MOAZZEN-AHMADI, Department of Physics and Astronomy, University of Calgary, 2500 University Dr., N.W., Calgary, Alberta T2N 1N4, Canada; A. R. W. MCKELLAR, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, K1A 0R6, Canada.

Infrared spectra of two isomers of the weakly bound OCS-CO₂ complex were observed using a tunable diode laser to probe a pulsed supersonic slit-jet. Spectra were recorded in the regions of OCS ₁ ( 2060 cm^-1) and CO_{2 3} ( 2349 cm^-1) fundamental stretching vibrations. The lowest energy isomer (isomer a ) was previously studied by microwave spectroscopy. Here we report the first infrared observation of isomer a and also detection of a new higher energy form (isomer b ). Structures were determined with the help of isotopic substitution. Both isomers are planar, with slipped near-parallel geometries. In isomer a , the intermolecular (centre of mass) separation is 3.55 Å and the C atom of the CO₂ is closer to the S atom of the OCS. In isomer b , the C atom of CO₂ slides closer to the O atom of OCS and the center of mass separation increases to 3.99 Å. 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 a and b , respectively, indicating that isomer a is indeed more bound than isomer b .