High resolution quantum cascade laser studies of the _3 band of methyl fluoride in solid para-hydrogen

摘要

Spectra of solid para-H_2 doped with CH_3F at 1.8K are studied in the _3 region (~1040 cm~(-1)) using a quantum cascade laser source. As shown previously, residual ortho-H_2 in the sample (~1000 ppm) gives rise to distinct spectral features due to clusters of the form CH_3F-(ortho-H_2)_N, with N = 0, 1, 2, 3, etc. Brief annealing at 7K is found to give narrower spectral lines (≥0.006 cm~(-1)) than conventional (5K) annealing, and causes the N 3 and 4 lines to fragment into two or more components. The N 3 line is observed to be particularly stable and persistent. The N = 0 line (no ortho-H_2 neighbors) is resolved into two closely spaced (≈0.007 cm~(-1)) components which are assigned to the K = 0 and 1 states of CH_3F rotating around its C_(3v) symmetry axis (ortho- and para-CH _3F, respectively). Similar K-structure is also evident for other lines. Weak but persistent features (N 1/2 lines) are observed mid way between N 0 and 1.