Knowledge Bank

Jet-cooled laser excitation spectra of the $A~2A\prime -X~2A\prime \prime$ bad system of the $FS2$ free radical will be presented. This study represents the first spectroscopic observation of this species, which may be important in the dry etching of integrated circuits using $SF6$ low pressure plasmas. High resolution spectra of several bands have been rotationally analyzed yielding precise molecular constants and structural data for the ground and electronically excited states. A few axis-switching transitions with $\Delta 2=0$ have been assigned, consistent with a calculated axis-switching angle of $5.3\circ$. The electronic transition has $T\infty =14.922cm-1$ and involves excitation of a non-boding electron localized on the terminal sulfur to a $\pi +$ orbital delocalized over the S-S bond.