High-Resolution Fourier Transform Infrared Spectrum of the ν 2/ν 5 Fundamental Band System of 13CH 3F

Abstract

The vibration-rotational bands ν 2 and ν 5 of gaseous fluoromethane 13CH 3F were measured in the region 1200-1700 cm −1 at an unapodized resolution of 0.0041 cm −1 using an interferometric spectrometer Bruker IFS 120 HR. Almost 3000 lines were assigned including 381 lines of the Δ k = ±2 perturbation-allowed transitions to the doubly degenerate vibrational state v 5 = 1. Combination differences were generated for the ground state from the allowed and "forbidden" transitions of the ν 2 and ν 5 bands. They were used in a simultaneous fit with the previously measured frequencies of the ground state rotational transitions and the combination differences generated from the ν 3 band (D. Papoušek, Z. Papoušková, Yen-Chu Hsu, P. Pracna, S. Klee, M. Winnewisser, and J. Demaison, J. Mol. Spectrosc. 159, 62-68, 1993) to improve the values of the ground state spectroscopical parameters of 13CH 3F. The upper state parameters were determined by fitting simultaneously the infrared data with the frequencies of the rotational transitions in the v 2 = 1 and v 5= 1 levels (preceding paper), using a variational approach with the constrained values of the ground state parameters.