RC13		15min11:57

K. HOSHINA, H. KOHGUCHI AND Y. ENDO, Department of Pure and Applied Sciences, College of Arts and Sciences, The University of Tokyo, 153 Tokyo, Japan; Y. OHSHIMA, Department of Chemistry, Graduate School of Science, Kyoto University, 606-01 Kyoto, Japan.

Laser-induced-fluorescence spectra of the C₄H and C₄D radicals have been observed for the first time. The molecules were generated in a supersonic jet by an electric discharge of C₂H₂ or C₂D₂ diluted in Ar. Fourteen and thirteen vibronic bands were observed for C₄H and C₄D respectively, in the near UV region(24000 - 25000 cm^-1). The bands were assigned to the ²-² or ²-² type, and several ²-² bands were subjected to rotational analyses. The determined rotational constants for the lower state agree with those for C₄H/C₄D in the ground vibrational level in the X² state, which were reported in a previous microwave study . The spin-orbit splittings in the ²-² bands are 16 and 12 cm^-1 for C₄H and C₄D, respectively, leading a conclusion that the excited electronic state for the observed band system is ². The present observation is consistent with a recent CASSCF study, which predicted the B² state with the excitation energy of 24500 cm^-1.