The ν2 fundamental band of triplet CH2

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Abstract
The ν2 (bending) fundamental band of CH2 in its X̃ 3B1 ground electronic state has been studied using tunable diode laser spectroscopy and also the LMR (laser magnetic resonance) technique in the 800–911 cm−1 and 1030–1173 cm−1 regions. For the diode laser study, a multiple‐traversal absorption cell was used with Zeeman modulation, and the CH2 radicals were produced by a mild discharge in a flowing mixture of ketene (∼0.3 Torr) and helium (∼2 Torr). Under these conditions, the apparent lifetime of CH2 following cutoff of the discharge was about 1 ms. A total of 53 new transitions with rotational quantum numbers up to N=10, K‘a =3, and Ka =2 were observed to add to the 11 transitions previously measured in this band. A combined analysis of the present data and all the previous pure rotational and ν2 band results on CH2 has yielded an improved set of molecular parameters, including the first determination of centrifugal distortion effects for the dominant spin–spin interaction parameter, D. The present data have also been used in a comprehensive new analysis of triplet methylene rotation–vibration energies using the nonrigid bender Hamiltonian by Bunker et al. in an accompanying paper.