title: High-resolution spectroscopy of the C-N stretching band of methylamine.
abstract: The C-N stretching infrared fundamental of CH(3)NH(2) has been investigated by high-resolution laser sideband and Fourier transform synchrotron spectroscopy to explore the energy level structure and to look for possible interactions with high-lying torsional levels of the ground state and other vibrational modes. The spectrum is complicated by two coupled large-amplitude motions in the molecule, the CH(3) torsion and the NH(2) inversion, which lead to rich spectral structure with a wide range of energy level splittings and relative line intensities. Numerous sub-bands have been assigned for K values ranging up to 12 for the stronger a inversion species for the v(t) = 0 torsional state, along with many of the weaker sub-bands of the s species. The C-N stretching sub-state origins have been determined by fitting the upper-state term values to J(J + 1) power-series expansions. For comparison with the ground-state behaviour, both ground and C-N stretch origins have been fitted to a phenomenological Fourier series model that produces an interesting pattern with the differing periodicities of the torsional and inversion energies. The amplitude of the torsional energy oscillation increases substantially for the C-N stretch, while the amplitude of the inversion energy oscillation is relatively unchanged. Independent inertial scale factors ρ were fitted for the torsion and the inversion and differ significantly in the upper state. The C-N stretching vibrational energy is determined to be 1044.817 cm(-1), while the effective upper state B-value is 0.7318 cm(-1). Several anharmonic resonances with v(t) = 4 ground-state levels have been observed and partially characterized. A variety of J-localized level-crossing resonances have also been seen, five of which display forbidden transitions arising from intensity borrowing that allow determination of the interaction coupling constants.
authors.affiliation: Centre for Laser, Atomic and Molecular Studies (CLAMS), Department of Physics, University of New Brunswick, Saint John, New Brunswick E2L 4L5, Canada. lees@unb.ca
authors.forename: Ronald M
authors.initials: RM
authors.lastname: Lees
authors.forename: Zhen-Dong
authors.initials: ZD
authors.lastname: Sun
authors.forename: B E
authors.initials: BE
authors.lastname: Billinghurst
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry; D007834:Lasers; D008744:Methylamines / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D008744:Methylamines; D002245:Carbon Dioxide; C027451:methylamine