Knowledge Bank

A new method for the analysis and characterization of a large number of rotational-torsional transitions of methanol and its isotopic variants is presented which is based on our earlier work that used a direct diagonalization of an internal axis method $Hamiltonian.1$ In it the analysis of the A and E symmetry subspecies has been separated and selected cross terms between torsional and rotational operators have been added to the Hamiltonian. Previous analyses of these molecules resulted in an overall rms deviation of 1-2 MHz for transitions with $J\le 8$ in the first three torsional states. The data sets have now been expanded to include transitions of higher J and K in the first three torsional states without the introduction of systematic model error as was the case with the earlier model. The results presented here have an rms deviation of $\sim 100$ kHz, which is on the order of experimental error. As a consequence of this new approach, the predictive powers of this model have been greatly enhanced and now provide a means for the accurate characterization of the rotational-torsional spectrum of methanol and its isotopic variants.