15min:

JEFFREY A. GRAY, Department of Chemistry, Ohio Northern University, Ada, OH 45810; THOMAS B. SETTERSTEN AND ROGER L. FARROW, Combustion Research Facility, Sandia National Labs, Livermore, CA 94551.

The predissociated B ²A₁' state of CH₃ has a sub-picosecond lifetime,^a which causes all absorption bands in the B~²A₁' X ²A₂'' system to be unstructured, and molecular constants for the B state must be inferred from analysis of partly resolved lines in the corresponding bands of CD₃.^b We observe isolated rotational transitions in the B~ ~X origin band of CH₃ using two-color resonant four-wave mixing (TC-RFWM) spectroscopy with an IR laser that excites known lines in the ₃ fundamental band^c to label specific N, K levels of the X state. Analysis of TC-RFWM spectra involves fitting complex Lorentzian lineshapes and yields an updated value of 46,241 \pm 5 cm^-1 for T₀ of the B state.

^a S. G. Westre, P. B. Kelly, Y. P. Zhang, and L. D. Ziegler, shape J. Chem. Phys. 94, 270-276 (1991).
^b G. Herzberg, shape Proc. R. Soc. London Ser. A 262, 291-317 (1961).
^c T. Amano, P. F. Bernath, C. Yamada, Y. Endo, and E. Hirota, shape J. Chem. Phys. 77, 5284-5287 (1982).