CH 318OH: FIR laser line frequency measurements and assignments

Abstract

Observations of far-infrared (FIR) laser emission and assignments of FIR laser lines have been reported in the literature for the O-18 isotopomer of methanol optically pumped by CO 2 lasers. So far, wavelengths have been measured for 100 FIR laser lines, and assignments for 26 of these lines have been proposed. However, some assignments were uncertain, with several possible alternatives, notably for the lines pumped by the 10R(20) CO 2 line. The present work combines new accurate FIR laser heterodyne frequency measurements with the results of Fourier transform spectroscopic studies of the CO-stretching and FIR torsion-rotation bands of CH 3 18 OH in a detailed analysis of the FIR laser emission. Precise frequencies have been determined for 22 of the laser lines, and five new laser lines have been observed. The spectroscopic results have led to unambiguous assignments for 20 of these lines and their confirmation through transition combination loops. The assignments of 13 of the lines are given for the first time. With the new results, the enigmatic 10R(20) situation has been almost completely resolved.