Infrared spectra of CH3F(ortho-H2)n clusters in solid parahydrogen

The formation of CH3F(ortho-H-2)(n) clusters in rapid vapor deposited solid molecular hydrogen containing low concentrations of CH3F and ortho-H-2 has been investigated using high-resolution Fourier transform infrared spectroscopy of the C-F stretching mode (nu(3)) of the CH3F chromophore. Distributions of CH3F(ortho-H-2)(n) clusters ranging in size from n=0 to n=12 are synthesized in para-H-2 crystals by systematically varying the ortho-H-2 concentration between 100 to 20 000 parts per million. The rotational motion of CH3F is quenched in solid para-H-2; this simplifies the spectrum such that a single sharp transition is observed for each cluster. In the fundamental nu(3) region, the spectrum consists of a series of well-separated peaks shifted toward lower energy with increasing numbers of nearest neighbor orthohydrogen molecules. The CH3F(ortho-H-2)(n) clusters are also investigated in the nu(3) overtone region and for analogous transitions of the CD3F(ortho-H-2)(n). Theoretical calculations based on an electrostatic interaction potential qualitatively reproduce the measured vibrational and isotopomer dependence of the spectra. (C) 2003 American Institute of Physics.