Microwave spectrum of methyl amine: Assignment and analysis of the first torsional state

Abstract

Abstract The microwave absorption spectrum of methyl amine has been reinvestigated in the range from 7 to 90 GHz, with the aim of analyzing the first torsional state in more detail. By combining the newly obtained microwave data with the far-infrared and microwave data already available, it was possible to make and analysis of the tunneling-rotational levels of the first torsional state in which three types of Δ K = ±1 elements were introduced into the Hamiltonian matrix described in the group-theoretical formalism developed previously. The present global fit uses 38 molecular parameters (three fewer than previously) to describe 714 transitions involving tunneling-rotational levels of the first excited torsional state (57 more than previously). It resulted in a satisfactorily small standard deviation of 0.00095 cm −1 (almost the same as previously) for J ≦ 30 (five J values higher than included previously). On the basis of this fit, avoided crossings between K = 0 and 1 levels belonging to A and B species in the molecular symmetry group G 12 are discussed in detail for the first time. Stark effect data, remeasured during the present study, are also examined in connection with the Δ K = ±1 interaction.