15min:

M. REZAEI, J. NOROOZ OLIAEE, N. MOAZZEN-AHMADI, Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada; A. R. W. MCKELLAR, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada.

Infrared spectra of carbon disulfide trimer formed in a pulsed supersonic slit-jet expansion are obtained via direct absorption of a tuneable diode laser in the region of the CS_{2 3} fundamental band ( 1535 cm^-1). Two bands sharing the same lower state were assigned to (C³²S₂)₃. These correspond to the two infrared active vibrations (a parallel and a perpendicular band) of the constituent CS₂ asymmetric stretches. The weaker perpendicular band is centered at 1524.613 cm^-1. It is shifted by -10.74 cm^-1 with respect to the free CS₂ monomer. The parallel band which is significantly stronger is centered at 1545.669 cm^-1. It has a vibrational shift of +10.31 cm^-1. The transitions with K 3n and those with J= odd and K=0 in the ground state are absent in both bands. This rigorously establishes that this isomer of carbon disulfide trimer has D₃ symmetry. Thanks to the symmetry, only two parameters, the C-C distance and the angle between a monomer axis and the plane containing the C atoms, are required to fully define the structure of the trimer. These were determined to be 3.811 Å and 61.8^\circ, respectively. In addition, a parallel band corresponding to a single ³⁴S substitution was observed around 1544.46 cm^-1. Results from this band are in complete agreement with those of the two bands for (C³²S₂)₃.