| 摘要: | The G6 group-theoretical high-barrier formalism developed previously for internally rotating and inverting CH3NHD is used to interpret the abnormal torsional splittings in the S1 state of acetaldehyde for levels 140-150, 140-151, and 140-152, where 140- denotes the upper inversion tunneling component of the aldehyde hydrogen and 15 denotes the methyl torsional vibration. This formalism, derived using an extended permutation-inversion group G6m, treats simultaneously methyl torsional tunneling, aldehyde-hydrogen inversion tunneling and overall rotation. Fits to the rotational states of the four pairs of inversion-torsion vibrational levels (140+150A,E, 140-150A,E), (140+151A,E, 140-151A,E), (140+152A,E, 140-152A,E), and (140+153A,E, 140-153A,E) are performed, giving root-mean-square deviations of 0.003, 0.004, 0.004, and 0.004 cm-1, respectively, which are nearly equal to the experimental uncertainty of 0.003 cm-1. For torsional levels lying near the top of the torsional barrier, this theoretical model, after including higher-order terms, provides satisfactory fits to the experimental data. The partially anomalous K-doublet structure of the S1 state, which deviates from that in a simple torsion-rotation molecule, is fitted using this formalism and is shown to arise from coupling of torsion and rotation motion with the aldehyde-hydrogen inversion. |
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