Second torsional state of methylamine from high resolution IR spectra

The high resolution infrared spectrum of methylamine has been analyzed in the 40-720 cm−1 region (the ν15 = 2←1 hot and ν15 = 2←0 overtone bands) with a resolution of 0.00125 cm−1. More than 14,400 rovibrational transitions (out of 133,000 spectral lines) for 0 ≤ K ≤ 13 and K ≤ J ≤ 40 have been assigned using an original Loomis-Wood program dedicated to methylamine. A global fit of the torsional hot and overtone transitions has been carried out. The assigned transitions were fit to a single state model based on the group theoretical formalism of Hougen and Ohashi, which for the second torsional state seems to be at the limit of applicability. The standard deviation of the fit with K ≤ 11 and J ≤ 40 to 94 parameters was 0.006 cm−1.