15min:

MING-WEI CHEN, JINJUN LIU, DMITRY G. MELNIK AND TERRY A. MILLER, Laser Spectroscopy Facility, Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, Ohio 43210.

Methoxy radical, a key component in both atmospheric and combustion chemistry, has attracted spectroscopic interest for more than twenty years. Microwave measurements of CH₃O\footnoteY. Endo, S. Saito, and E. Hirota, J. Chem. Phys. , \underline\textbf81, 122 (1984) and CD₃O\footnoteT. Momose, Y. Endo, and E. Hirota, unpublished data. with precision on the kHz scale have determined the X²E parameters. Jet-cooled laser induced fluorescence (LIF) spectra have also been observed by our group for both CH₃O and CD₃O, with high-resolution ( ~250 MHz) and high-accuracy ( ~50 MHz), for the 3²₀ and 6¹₀ bands of the A²A₁ - X²E_3/2 electronic transition. Since the ground state component E_1/2 is ~60 cm^-1 energetically higher than the E_3/2 spin component, the X²E_1/2 state is not thermally populated in a jet-cooled environment. However, our complementary stimulated emission pumping (SEP) experiment directly interrogates the X²E_1/2 level of CH₃O and CD₃O by depleting the fluorescence from A²A₁ 3² excited levels. It has now been performed with the same resolution and accuracy as the LIF work. The global analysis of the microwave^b,c, 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 CH₃O, ¹³CH₃O\footnoteT. Momose, Y. Endo, E. Hirota, and T. Shida, J. Chem. Phys. , \underline\textbf88, 5338 (1988), and CD₃O allows us to separate first-order from second-order electronic and vibrational contributions based upon the isotopic dependencies of the effective ground state parameters, e.g. the Jahn-Teller parameters h₁ and h₂ , spin-rotation parameters, etc.