Knowledge Bank

The infrared diode laser spectrum of the $H3$ band of the silyl radical $(SiH3$), corresponding to the degenerate Si-H stretching mode, has been observed in the region of 2000 $2300cm-1$. The $SiH3$ radical was generated in the positive column of the discharge in phenyl silane diluted with Ar, and detected by the discharge modulation technique. The optimum frequency for the ac discharge was 50 Hz, and the discharge current was about 100 mA p-p. Much stronger $SiH4$ lines, which were observed abundantly in the present region when $SiH4$ was used as a parent substance, were almost absent with phenyl silane as a parent substance. In total 35 lines (24 , 7 , and $4rQ$ branch transitions) were identified for the fundamental band. Most of the $R-$ and $P-$ branch lines were observed as doublet with a separation of about $0.04cm-1$ due to the inversion doubling, however the Q-branch lines were observed to be split into quartet due to the spin-rotatation doubling as well as the inversion doubling. Preliminary molecular constants for the upper vibrational state are $B=4.721(26)$, $C=2.800(16)$, $D1=0.000391(81)$, $Dyx=-0.00080(14)$, $C\zeta =0.1198(27)$, $\eta 1=-0.00101(22)$, and $\nu 0=2185.240(18)cm-1$, where the constants for the ground state were fixed to the values in Ref. 1. Slightly large residuals in the fit ($\sim$300 MHz) may be attributed to the perturbations caused by the Coriol is interaction between the $H1$ and $H3$ vibrations.