15min:

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

Silylene (SiH₂) is a silicon analogue of methylene (CH₂). The number of spectroscopic studies on SiH₂ is much smaller compared with that on CH₂ is small. Until now, only the X ¹A₁, A ¹B₁, and a ³B₁ states have been experimentally investigated. Recently, energetics and equilibrium structure of the next low-lying B ¹A₁ state was studied by high-level calculations by Yamaguchi et al . However, a corresponding electronic state has not yet been observed. In the course of our SEP spectroscopic study on highly excited vibrational levels of SiH₂, we have identified several bands that can be assigned as transitions to the B state for the first time. \par When a J=0 rotational level of the A state was used as an intermediate level of the OODR measurement, several vibronic bands of 1100 -- 1200 cm^-1 interval were observed in the energy region of 28000 -- 30100 cm^-1 above the X state. Based on a rotational selection rule and a predicted bending vibrational frequency, we assigned these bands as an odd-v₂ progression. This means that the SiH₂ in the B state behaves as a linear molecule. To confirm our assignment, it is necessary to observe OODR spectra via a K_a=1 rotational level. To avoid a difficulty in measuring desired OODR transitions due to a predissociation in the A state of SiH₂, an OODR spectroscopy of SiD₂ was also carried out. We have succeeded in measuring the OODR transitions to the B state of SiD₂ and determined the value of T₀ of SiD₂ to be 27214.11 cm^-1. Our observation on SiD₂ confirmed the quasi-linear behavior in the B state. Details of our observation will be presented in the paper.