Rotationally Resolved $\tilde{A}^2$A$_1$ - $\tilde{X}^2$E Electronic Spectra of Symmetric Methoxy Radicals: CH$_3$O and CD$_3$O

Methoxy radical has attracted spectroscopic interest for more than twenty years. Microwave measurements of CH$_3$O and CD$_3$O with precision on the kHz scale have determined the $\tilde{X}^2$E parameters. Jet-cooled laser induced fluorescence (LIF) spectra have also been observed by our group with high-resolution ($\Delta\nu\sim$250 MHz) and high-accuracy ($\Delta\sigma\sim$50 MHz), for the 3$^2_0$ and 6$^1_0$ bands of the $\tilde{A}^2$A$_1$ - $\tilde{X}^2$E$_{3/2}$ electronic transition. Since the ground state component E$_{1/2}$ is $\sim$60 cm$^{-1}$ energetically higher than the E$_{3/2}$ spin component, the $\tilde{X}^2$E$_{1/2}$ state is not thermally populated in a jet-cooled environment. However, our complementary stimulated emission pumping (SEP) experiment with the same resolution and accuracy as the LIF work directly interrogates the $\tilde{X}^2$E$_{1/2}$ level of CH$_3$O and CD$_3$O by depleting the fluorescence from the $\tilde{A}^2$A$_1$ 3$^2$ levels. The global analysis of the microwave, LIF, and SEP data breaks correlations in the microwave data and provides better determinations for the $\tilde{X}$ and $\tilde{A}$ states' parameters. Comparison of the values for CH$_3$O, $^{13}$CH$_3$O, and CD$_3$O allows us to separate first-order from second-order electronic and vibrational contributions based upon the isotopic dependencies of the effective ground state parameters.