Knowledge Bank

Optical excitation of some molecules have been obtained by using a $CO2$ laser. We report the observation of vibrational excitation in $SF6$. Low $CO2$ laser power density (about $0.5W/mm2$) induce strong excitation in $SF6$ resulting in a steady state nearly half-depopulated ground level and large population of low-lying vibrational levels. The experiments were done at the pressure range 2 to 50 torr. $CO2$ laser energy on the P20 line is absorbed on the 0-1 and probably also on the 1-2 transitions of the $\nu 3$ vibrational mode. Induced populations of the $\nu 3$ and $2\nu 3$ levels were observed through detection of the fluorescence. Fluorescence arising from the $\nu 4$ mode was also observed which indicates collisional excitation of this mode through $\nu 3$. Populations of the lowest vibrational levels have been evaluated from absorption measurements. Collisional relaxation times for the transfer of vibrational energy from the $\nu 3$ mode to the other modes have been investigated.