Observation of the $\widetilde{A}-\widetilde{X}$ Electronic Transition of the Jet-Cooled Methyl Peroxy Radical by High Resolution CRDS

Reactive intermediates are of crucial importance both for combustion and atmospheric chemistry. By using our new home made Fourier Transform limited (10--30~MHz) Ti:Sa laser source we have probed the vibrationless level of the first electronic state (in the near-IR range) of both ${\rm CH}_{3}{\rm OO}$ and ${\rm CD}_{3}{\rm OO}$ radical species. The radicals are formed inside a ${\rm Ne/He/O}_{2}/{\rm CH}_{3}{\rm I}$ plasma created by a DC or a RF electrical discharge. The supersonic jet expansion necessary for the rotational cooling ($\sim20\,{\rm K}$) is obtained by a pulsed slit nozzle ($\sim50\times0.5\,{\rm mm}^{2}$). The near-IR radiation, obtained by Stimulated Raman Scattering (SRS) is injected inside a high finesse cavity. A sensitivity of the order of $\sim20\times10^{-9}\,/{\rm pass}/\sqrt{{\rm Hz}}$ is currently obtained. Spectrum with a resolution $\sim350\,{\rm MHz}$ for ${\rm CD}_{3}{\rm OO}$ clearly shows rotational and spin-rotation structure with effects of the internal methyl group rotation possibly evolved.