The NH$_2$ scissors band of methylamine

Abstract

For the first time the $\nu_4$ NH2 scissors band has been assigned in a high-resolution infrared spectrum. A rotationally resolved spectrum of methylamine was recorded using two infrared spectroscopic techniques. A White-type multi-pass cell device coupled to the Bruker IFS 125 HR Fourier transform spectrometer was implemented on the AILES beamline at the SOLEIL synchrotron facility and a room-temperature spectrum of the whole band in the region of 1540-1710 cm-1 was recorded with a resolution of 0.001 cm-1. Then, a low-temperature high-resolution spectrum in the 1622.5-1655.6 cm-1 range of Q and R branches of the $\nu_4$ band was recorded using a quantum cascade laser spectrometer. Preliminary assignment was carried out in the NH2 scissors band region, and about 2200 transitions for $K$ from 0 to 6 have been assigned for A, B, and E1 symmetry species. The simultaneous fit of assigned lines using a group-theoretical effective Hamiltonian was not successful; instead simple polynomial series expansions were used for each symmetry and $K$ value.

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