Inversion and internal rotation in methyl-d-amine: Microwave spectrum |
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Authors: | Keietsu Tamagake Masamichi Tsuboi |
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Institution: | Faculty of Pharmaceutical Sciences, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan |
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Abstract: | The microwave spectrum of CH2DNH2 has been observed in the 8–74 GHz region. The spectrum shows that this molecule takes essentially two distinguishable conformers, trans and gauche forms, although a small amount of coupling between them can be detected. For each line of the trans form a small inversion splitting has been found. It is 93.97 MHz at K = 0 and a periodic function of K. The mean frequencies of the inversion pairs of lines are well explained as the frequencies of a rigid rotor. The gauche spectrum is extremely complicated; each rotational line splits into four because of inversion and gauche-gauche tunneling interactions. The analysis was carried out based on the theory developed in the preceding paper. Tunneling energy parameters of internal-rotation, ?gg and ?tg, and inversion, δgg and δtg, were determined as ?gg = 3476.6 MHz, ?tg = 3233.1 MHz, δgg = 2790.6 MHz and δtg = 3052.7 MHz. Energy difference between trans and gauche conformers ΔEtg was estimated to be 7.060 cm?1 from these values of parameters and also on the basis of the observed anomaly in the Q branch series of trans form which is due to an accidental degeneracy between the K = 1 level of trans and K = 2 level of gauche. The effects on the internal-rotation of other internal motions have also been discussed. |
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