Knowledge Bank

Methoxy radical, a key component in both atmospheric and combustion chemistry, has attracted spectroscopic interest for more than twenty years. Microwave measurements of CH$3$O}, \underline{\textbf{81}}, 122 (1984)}} and CD$3$O}}} with precision on the kHz scale have determined the $X~2$E parameters. Jet-cooled laser induced fluorescence (LIF) spectra} {61 International Symposium on Molecular Spectroscopy, (2006)}} have also been observed by our group for both CH$3$O and CD$3$O, with high-resolution ($\Delta\nu\approx$250MHz)andhigh-accuracy($\Delta\sigma\approx$50MHz),forthe3$^2_0$ and 6$\mathrm{01}$ bands of the $A~2$A$1$ - $X~2$E$\mathrm{<mrow\; data-mjx-texclass="ORD">3<mrow\; data-mjx-texclass="ORD">/</mrow>2</mrow>}$ electronic transition. Since the ground state component E$\mathrm{<mrow\; data-mjx-texclass="ORD">1<mrow\; data-mjx-texclass="ORD">/</mrow>2</mrow>}$ is $\approx$60cm$^{-1}$ energetically higher than the E$\mathrm{<mrow\; data-mjx-texclass="ORD">3<mrow\; data-mjx-texclass="ORD">/</mrow>2</mrow>}$ spin component, the $X~2$E$\mathrm{<mrow\; data-mjx-texclass="ORD">1<mrow\; data-mjx-texclass="ORD">/</mrow>2</mrow>}$ state is not thermally populated in a jet-cooled environment. However, our complementary stimulated emission pumping (SEP) experiment directly interrogates the $X~2$E$\mathrm{<mrow\; data-mjx-texclass="ORD">1<mrow\; data-mjx-texclass="ORD">/</mrow>2</mrow>}$ level of CH$3$O and CD$3$O by depleting the fluorescence from $A~2$A$1$ 3$2$ excited levels. It has now been performed with the same resolution and accuracy as the LIF work. The global analysis of the microwave, LIF, and SEP data breaks correlations in the microwave data and provides better determinations for the $X~$ and $A~$ states' parameters. Comparison of the values for CH$3$O, $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$CH$3$O}, \underline{\textbf{88}}, 5338 (1988)}}, 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, \textit{e.g.} the Jahn-Teller parameters \textit{h$1$} and \textit{h$2$}, spin-rotation parameters, etc.