15min:

H. ISHIKAWA, Y. MURAMOTO AND N. MIKAMI, Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.

SiH₂ is one of the simplest silicon containing radicals. Similarity and dissimilarity to CH₂ radical are very interesting from both chemical and spectroscopic points of view. Renner-Teller interaction between the A~¹B₁ and the X~¹A₁ states and an energy separation between the X~¹A₁ and the a~³B₁ states are very important issues in spectroscopy. An analysis of highly excited vibrational levels in the X state should provide some valuable information about them. Thus, we have carried out stimulated emission pumping (SEP) spectroscopy on SiH₂. \par In the present study, a pulsed discharge nozzle was used to generate jet-cooled SiH₂ radical. Precursor of SiH₂ radical was phenylsilane. The 0₀₀ rotational levels of the A (060) and (070) levels were used as intermediate levels in the present SEP spectroscopy. \par Until now, vibrational levels with v₂ up to 4 (E_vib \le 4000~ cm^-1) have been observed . In the present study, 22 vibrational levels in the energy region of 4800 -- 8000 cm^-1 were observed. Due to strong 2 ₂:1 ₁ Fermi and 2 ₁:2 ₃ Darling-Dennison resonances, vibrational levels having the same polyad quantum number, P=2v₁+v₂+2v₃, construct polyad structures. The vibrational levels observed belong to polyads of P=5-8. Taking these resonance into account, vibrational analysis of the SiH₂ radical was carried out. In the present analysis, vibrational constants, x₁₃ and x₂₃, could be determined experimentally, for the first time. Preliminary values are -74.83 cm^-1 and -17.58 cm^-1, respectively. Details of the vibrational analysis will be discussed at the presentation. \par