(CH3OH)-O-18 - FIR LASER LINE FREQUENCY MEASUREMENTS AND ASSIGNMENTS

Observations of far-infrared (FIR) laser emission and assignments of F IR laser lines have been reported in the literature for the O-18 isoto pomer of methanol optically pumped by CO2 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 uncerta in, with several possible alternatives, notably for the lines pumped b y the 10R(20) CO2 line. The present work combines new accurate FIR las er heterodyne frequency measurements with the results of Fourier trans form spectroscopic studies of the CO-stretching and FIR torsion-rotati on bands of CH3 18OH in a detailed analysis of the FIR laser emission. Precise frequencies have been determined for 22 of the laser lines, a nd five new laser lines have been observed. The spectroscopic results have led to unambiguous assignments for 20 of these lines and their co nfirmation 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.