INFRARED SPECTRA OF CO$_2$ - H$_2$ COMPLEXES
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Date
2005
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Ohio State University
Abstract
Infrared spectra of weakly-bound CO$_2$-H$_2$ complexes have been studied in the region of the CO$_2$ \nub{3} asymmetric stretch, using a tunable diode laser probe and a pulsed supersonic jet expansion. For CO$_2$-$para$H$_2$, results were obtained for three isotopic species, $^{12}$C$^{16}$O$_2$, $^{13}$C$^{16}$O$_2$, and $^{12}$C$^{18}$O$_2$. These spectra were analyzed using an asymmetric rotor Hamiltonian, with results that resembled those obtained previously for OCS- and N$_2$O-$para$H$_2$ [1], except that half the rotational levels were missing due to the symmetry of CO$_2$ and the spin statistics of the $^{16}$O or $^{18}$O nuclei (as in the similar case of CO$_2$-He [2]). The CO$_2$-$para$H$_2$ complex has a T-shaped structure with an intermolecular distance of about 3.5 \AA, and the CO$_2$ \nub{3} vibration exhibits a small red shift (-0.20 \wn) in the complex. For CO$_2$-$ortho$H$_2$, more complicated spectra were observed which could not be assigned, in contrast to OCS- and N$_2$O-H$_2$ where the $para$H$_2$ and $ortho$H$_2$ spectra were similar, though distinct. \vskip 0.3 truecm [1] J. Tang and A.R.W. McKellar, \textit{J. Chem. Phys.} \textbf{116}, 646 (2002); \textbf{117}, 8308 (2002). [2] M.J. Weida, J.M. Sperhac, D.J. Nesbitt, and J.M. Hutson, \textit{J. Chem. Phys.} \textbf{101}, 8351 (1994).
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Author Institution: Steacie Institute for Molecular Sciences, National Research; Council of Canada, Ottawa, Ontario K1A 0R6, Canada