The rotational and vibrational dynamics of argon-methane. I. A theoreticalstudy

Reported here is a theoretical calculation of the spectrum of the argon-met hane complex based upon a previously reported ab initio potential energy su rface [T. G. A. Heijmen et al., J. Chem. Phys. 107, 902 (1997)]. The irregu lar rotational structure observed in the spectrum is traced to a combinatio n of the fact that the excited vibrational state of the methane has vibrati onal angular momentum and the methane rotates nearly freely within the comp lex. The theoretical spectrum is compared qualitatively with the experiment al results obtained using the optothermal method, a more complete discussio n of which is given in a companion paper, hereafter referred to as paper II . (C) 1999 American Institute of Physics. [S0021-9606(99)01610-4].