ELECTRONIC SPECTRA OF THE METHYLIDYNES VCH AND TiCH.

1. M. Barnes, P.G. Hajigeorgiou, R. Kasrai, A.J. Merer and G.F. Metha, J. Amer. Chem. Soc, in press.Author Institution: University of British Columbia, 2036 Main Mall, Vancouver, B.C. Canada V6T 1Z1.The reaction of laser-ablated vanadium and titanium atoms with methane (or $methane-d_{4}$) under supersonic jet-cooled conditions allows spectra of the methylidynes VCH (VCD) and TiCH (TiCD) to be recorded by laser induced fluorescence. The VCH molecule has been shown to have a ${^{3}}\Delta_{1}$ ground state and three excited electronic states $({^{3}}\Delta, {^{3}}\Phi and {^{3}}\Pi)$ which give rise to bands in the $590 - 800 nm$ $region.^{1}$ Hyperfine-resolved laser induced fluorescence spectra of many of these bands have been assigned with a view to understanding the excited state electron configurations. Following direct pumping from the $01^{1}0$ and $01^{3}0$ vibronic components of the ground state bending vibration we have determined their separation as $2.6 cm^{-1}$. The substitution structure of the ground state is $r_{s}(V-C) = 1.702_{5} \AA; r_{s}(C-H) = 1.080 \AA.$ The TiCH molecule has been found to possess a ${^{2}}\Sigma^{+}$ ground state and several ${^{2}}\Pi$ vibronic excited states which give rise to bands in the $660 - 730 nm$ region. As in VCH the vibrational and rotational structure is heavily perturbed. Fits to high resolution ground state combination differences for TiCH and TiCD have given the substitution structure, $r_{s}(Ti-C) = 1.727_{7} \AA;\quad r_{s}(C-H) = 1.085 \AA.$ Very recently a new band system which may be due to CrCH has been discovered using a chromium target. A comparison of the structures, electron configurations and chemistry of the methylidynes will be presented