THE HIGH-RESOLUTION SPECTRUM OF ASH3(400) LOCAL MODE STATE - SYMMETRYREDUCTION AND ROTATIONAL RE-QUANTIZATION

The (400) stretching overtone band of AsH3 in the range of 7900-8100 c m(-1) was recorded by a Fourier transform spectrometer with a resoluti on of 0.01 cm(-1). The A(1) or A(2) - E degeneracy of the upper state rotational levels up to J' = 8 was observed. It is interesting to find that this spectrum resembles an A, C hybrid band of an asymmetric top and can be assigned by only one set of quantum numbers J, K-a and K-c . The rotational levels were determined by combination difference meth od and fitted in both the symmetric top and the asymmetric top models. In the latter case, the effective rotational constants A, B and C are in good agreement with the values predicted by a simple local mode mo del, indicating that the dynamical symmetry of AsH3 in the (400) local mode state has reduced to that of an asymmetric top. The transition f rom normal mode to local mode vibration from nu = 1 to 4 in AsH3 was d iscussed. (C) 1998 Elsevier Science B.V. All rights reserved.