15min:

A. R. W. MCKELLAR, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada.

Infrared spectra of weakly-bound CO₂-H₂ complexes have been studied in the region of the CO_{2 3} asymmetric stretch, using a tunable diode laser probe and a pulsed supersonic jet expansion. For CO₂-paraH₂, results were obtained for three isotopic species, ¹²C¹⁶O₂, ¹³C¹⁶O₂, and ¹²C¹⁸O₂. These spectra were analyzed using an asymmetric rotor Hamiltonian, with results that resembled those obtained previously for OCS- and N₂O-paraH₂ [1], except that half the rotational levels were missing due to the symmetry of CO₂ and the spin statistics of the ¹⁶O or ¹⁸O nuclei (as in the similar case of CO₂-He [2]). The CO₂-paraH₂ complex has a T-shaped structure with an intermolecular distance of about 3.5 Å, and the CO_{2 3} vibration exhibits a small red shift (-0.20 cm^-1) in the complex. For CO₂-orthoH₂, more complicated spectra were observed which could not be assigned, in contrast to OCS- and N₂O-H₂ where the paraH₂ and orthoH₂ spectra were similar, though distinct.

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[1] J. Tang and A.R.W. McKellar, J. Chem. Phys. \textbf116, 646 (2002); \textbf117, 8308 (2002).

[2] M.J. Weida, J.M. Sperhac, D.J. Nesbitt, and J.M. Hutson, J. Chem. Phys. \textbf101, 8351 (1994).