ANALYSIS OF THE QUASI-LINEARITY OF THE $\tilde{B}^{1} A_{1}$ STATE OF $SiH_{2}$ and $SiD_{2}$ RADICALS

$^{a}$ I. Tokue, private communicationAuthor Institution: Department of Chemistry, Graduate School of Science, Tohoku UniversityRecently we have observed OODR transitions terminating to the $\tilde{B}^{1} A_{1}$ state of $SiH_{2}$ and $SiD_{2}$. The OODR spectra observed indicate the quasi-linear behavior in the $\tilde{B}$ state based on the following features. Even or odd-$v_{2}$ levels exclusively appear in the OODR via an intermediate $K_{a}$=odd or even rotational level. This even/odd-$v_{2}$ progression is a typical pattern in the case of bent-linear transition. That is, $SiH_{2}$ acts as a linear molecule in the $\tilde{B}$ state and its bending vibration is doubly degenerate. Thus there exist a vibrational angular momentum $\ell$. The intensity pattern comes from a selection rule of a c-type transition; $\Delta(\ell - K_{a}) = \pm1$. Bending excited levels exhibit negative $g_{22}$-values. This is an indication of the double minimum potential. If an electronic state of interest was doubly degenerate, there would be a possibility of Renner-Teller effect. However, the $\tilde{B}$ state correlates to ${^{1}}\Sigma^{-}$ state in the linear configuration. Thus, this double minimum potential originates from the quasi-linearity. The height of the barrier to the linearity was calculated to be about $200 cm^{-1}. ^{a}$ It was confirmed that there are only $\ell (K_{a}) = 0$ rotational levels in the $v_{2} = 0$ level. This means that the $v_{2} = 0$ level is located above the barrier to linearity. It is very probable considering the very low barrier height. In addition, the absolute value of the $g_{22}$ constant rapidly decreases as the $v_{2}$-value increases. These observations strongly support the quasi-linearity of the $\tilde{B}$ state. In the presentation, results of the vibrational analysis on the quasi-linearity will be discussed