A simultaneous fit of vt = 0 and 1 torsion-wagging-rotational levels of CH3NH2 using a hybrid “tunneling and non-tunneling” Hamiltonian formalism “
Résumé
About 15,000 published transitions for methyl amine with J ≤ 40 have been refit using a hybrid program in which the single bondNH2 wagging motion is treated by a tunneling formalism, while the single bondCH3 internal-rotation motion is treated by the usual torsion-rotation Hamiltonian. Most of the fitted transitions are taken from published measurements. Compared to previous fits using the high barrier tunneling formalism for both motions, the present hybrid fit reduces the number of parameters in the Hamiltonian by about a factor of two, with essentially no increase in observed-minus-calculated residuals for the infrared transitions, and with an increase of about a factor of two for the microwave transitions. We showed that our approach can treat simultaneously for the first time the ground and first excited states of methylamine and can now be applied to (i) a much larger set of accurate vt = 1 microwave data, and (ii) infrared data on the vt = 2 ← 1 and 3 ← 2 torsional hot bands.
