A new analysis and additional measurements of the millimeter and submillimeter spectrum of methanol

Over 100 new spectral lines of gas-phase methanol in the millimeter and submillimeter region (viz. 150-1000 GHz) corresponding to rotational transitions in the two lowest torsional states have been measured and assigned. Some of these lines have been combined with spectral lines measured by previous investigators below 1000 GHz into a global data set consisting of 470 lines involving transitions with J ≤ 8 and v_t (torsional quantum number) ≤ 2, and then analyzed via a nonlinear least-squares procedure. The analysis involves supplementing the standard IAM Hamiltonian with a number of new distortion and "interaction" constants. Direct diagonalization has been employed in preference to an earlier perturbation scheme. The quality of the least-squares fit compares favorably with the previous quantum mechanical approach.