15min:

YUAN-PERN LEE, Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan; YU-JONG WU, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan; JON T. HOUGEN, Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8441.

Numerous studies have shown that methane and its various deuterated isotopologs CH_4-nD_n (n=0-4) can rotate relatively freely in solid parahydrogen. Less is known, however, of whether methyl groups can also carry out rotation (or internal rotation) in p -H₂, and even less is known of whether other large-amplitude motions involving hydrogen atoms (e.g., inversion or H transfer) can occur easily. The present talk, which is part of an attempt to systematically investigate these latter questions in National Chiao Tung University, presents infrared spectra for the nondegenerate ( ₁, ₂, ₃) and doubly degenerate ( ₄, ₅, ₆) vibrational fundamentals of CH₃F, together with a theoretical analysis strongly suggesting that CH₃F does indeed rotate about its symmetry axis ( a axis) in p -H₂, but does not rotate about axes perpendicular to the symmetry axis. The theoretical analysis makes use of the fact that a -axis rotation is expected to give rise: (i) to energy levels of the form E = AK², (ii) to first-order Coriolis interactions in degenerate vibrational states (E states), and (iii) to different nuclear spin functions for rovibrational A (K=0) and E (K=1 and 2) states. Experimental values for the relatively slow E A conversion rate in p -H₂ have also been determined. The results for CH₃F will be compared with our earlier results for CH₃OH.