IR rotational spectrum of methylamine

Abstract

Recent progress is reported on the assignment and fitting of a rotational spectrum of methylamine in the ground vibrational state and first and second torsional states. The high resolution infrared spectrum has been analyzed in the 40 to 360 cm−1 region with a resolution of 0.00125 cm−1. In the IR spectrum the complete RR and RQ series of rotational transitions were assigned up to high values of K and J, and for all symmetry species. For each set of rotational transitions a joint fit of all symmetry species has been carried out. The assigned transitions were fit to a single state model based on the group theoretical formalism of Hougen and Ohashi. The standard deviation of the fit for the ground state with K ≤ 20 and J ≤ 50 to 78 parameters was 0.00031 cm−1. The standard deviation of the fit for the first excited state with K ≤ 20 and J ≤ 45 to 89 parameters was 0.00066 cm−1, whereas for the second excited torsional state with K ≤ 14 and J ≤ 40 and with 95 parameters a standard deviation of 0.00207 cm−1 was obtained. About 8300 new infrared rotational transitions have been assigned in the ground, first and second torsional states using an original Loomis-Wood program dedicated to methylamine.