Improved molecular constants and empirical corrections for the torsional ground state of the CO stretch fundamental of CH 3OH

The CO stretch fundamental of CH ₃OH is analyzed on the basis of previously published diode laser spectra and data from optically pumped far-infrared laser emission. Improved values for I_b, I_c, and V₃ are presented, and I_a1 and I_a2 are determined separately. Energy levels are calculated, and empirical corrections tabulated, which show that the levels are heavily perturbed around K = 5. By including these corrections, as well as cubic effects in J( J + 1), infrared transition energies can be evaluated for K ≤ 10 and J ≤ 24 with an accuracy approaching the Doppler limit. The improved model is used for performing additional far-infrared laser line assignments.