INFRARED SPECTRUM OF THE STRONGLY CORIOLIS COUPLED $\nu_{2}$ AND $\nu_{4}$ VIBRATIONAL STATES OF ${CH_{3}}^{+}$

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1995

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Ohio State University

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The $\nu_{2}$ and $\nu_{4}$ bending vibrations of the methyl cation ${CH_{3}}^{+}$ are strongly coupled by Coriolis interaction because of the near degeneracy of the two vibrational modes. Ab initio theoretical $studies^{1,2,3}$ have predicted them to be within $1-20 cm^{-1}$. This is somewhat similar to the case of SiH3+ reported by Davies and $Smith^{4}$. The patchy coverage of the diode lasers and the strong Coriolis coupling make the analysis difficult. From $1503-1297 cm^{-1}, 95$ lines have been observed in a liquid cooled $He/H_{2}/CH_{4}$ plasma discharge using 5 diode lasers and velocity modulation. Six ${^{r}}Q(J, K = 0)$ transitions in the $\nu_{4}$ band were readily assigned since the $\nu_{4}$ levels involved in these transitions are free of the strong Coriolis interaction because of the absence of odd J, K = 0 levels in the $\nu_{2}$ vibrational state due to the Pauli exclusion principle. PP(J = K) transitions in the $\nu_{4}$ band are also free of the interaction and can be analyzed by using only diagonal matrix elements. A complete analysis of the bands is in progress and will be reported at the meeting. la. Feodor Lynen Fellow (Alexander von Humbolt Foundation).

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1. D.J. DeFrees and A.D. McLean, J. Chem. Phys. 82, 333 (1985) 2. P. Botschwina, in Ion and Cluster Ion Spectroscopy and Structure, edited by J.P. Maier (Elvier, Amsterdam, 1989) 3. W.P. Kraemer and V. Spirko, J. Molec. Spec. 149, 235 (1991) 4. P.B. Davies and D.M. Smith, J. Chem. Phys. 100, 6166 (1994)
Author Institution: The University of Chicago, Chicago, IL 60637-1403.; Technischen Universität Berlin, Berlin 10623 Germany.

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