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First High-Resolution Infrared Observation of the Symmetry-Forbidden Nu5 Band of 10B2H6



J.- M. Flaud, P Arcas, Walter J. Lafferty, H Berger, G Pawelke


Spectra of 10B monoisotopic diborane B2H6 have been recorded at high resolution (2 - 3 x 10-3 cm-1) by means of Fourier transform spectroscopy in the region 700 - 1300 cm-1. A thorough analysis of the Ņ 18 a-type, Ņ 14c-type and Ņ 5 symmetry forbidden band has been performed. Of particular interest, are the results concerning the Ņ5 symmetry forbidden band which is observed only because it borrows intensity through an a-type Coriolis interaction with the very strong Ņ18 infrared band located about 350 cm-1 higher in frequency. The Ņ5 band has been observed around 833 cm-1 and consists of a well resolved Q-branch accompanied by weaker P- and R-branch lines. Very anomalous line intensities are seen, with the low-Ka transitions being vanishingly weak. The determination of the upper state Hamiltonian constants proved to be difficult since the corresponding energy levels of each of the bands are strongly perturbed by nearby dark states. To account for these strong localized resonances, it was necessary to introduce the relevant interacting terms in the Hamiltonian. As a result the upper state energy levels were calculated satisfactorily, and precise vibrational energies and rotational and coupling constants were determined. In particular the following band centers were derived: Ņ05) = 832.8496 (70) cm-1,Ņ0 (Ņ14) = 977.57843 (70) cm-1, and Ņ0 (Ņ18) = 1178.6346 (40) cm-1. (A-type standard uncertainties (1sigma) are given in parenthesis.
Journal of Molecular Spectroscopy
No. 2


diborane, high resolution, infrared spectrum, symmetry forbidden band


Flaud, J. , Arcas, P. , Lafferty, W. , Berger, H. and Pawelke, G. (2000), First High-Resolution Infrared Observation of the Symmetry-Forbidden Nu<sub>5</sub> Band of <sup>10</sup>B<sub>2</sub>H<sub>6</sub>, Journal of Molecular Spectroscopy (Accessed February 29, 2024)
Created September 30, 2000, Updated October 12, 2021