DIRECT SPECTRAL EVIDENCE OF SINGLE-AXIS ROTATION AND ORTHO-HYDROGEN-ASSISTED NUCLEAR SPIN CONVERSION OF CH$_3$F IN SOLID PARA-HYDROGEN
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Date
2008
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Ohio State University
Abstract
Numerous studies have shown that methane and its various deuterated isotopologs CH$_{4-n}$D$_n$ $(n=0-4)$ can rotate relatively freely in solid parahydrogen. Less is known, however, of whether methyl groups can also carry out rotation (or internal rotation) in {\it p}-H$_2$, 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 ($\nu_1, \nu_2, \nu_3$) and doubly degenerate ($\nu_4, \nu_5, \nu_6$) vibrational fundamentals of CH$_3$F, together with a theoretical analysis strongly suggesting that CH$_3$F does indeed rotate about its symmetry axis ({\it a} axis) in {\it p}-H$_2$, but does not rotate about axes perpendicular to the symmetry axis. The theoretical analysis makes use of the fact that {\it a}-axis rotation is expected to give rise: (i) to energy levels of the form $E = AK^2$, (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 $\rightarrow$ A conversion rate in {\it p}-H$_2$ have also been determined. The results for CH$_3$F will be compared with our earlier results for CH$_3$OH.
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Author Institution: Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan; National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan; Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8441