The near infrared electronic spectrum of tungsten methylidyne, WCH

The laser excitation spectrum of tungsten methylidyne, WCH, has been recorded in the 12 000-15 400 cm(-1) region. A total of 14 vibronic bands of WCH and 16 bands of WCD have been observed in this region. Rotational analysis shows that the ground state is (X) over tilde 3/2((2) Delta), with the substitution structure r(0)(W=C)=1.7366(5) Angstrom and r(0)(C-H)=1.076(5) Angstrom. The excited vibronic levels have been assigned, on the basis of their WCH/WCD isotope shifts and their wavelength resolved fluorescence patterns, to three electronic states, (A) over tilde 3/2((2) Delta), (B) over tilde 1/2((2) Pi), and (C) over tilde 5/2(2 Phi), at 12 090, 13 392, and 14 110 cm(-1), respectively. The wavelength resolved fluorescence spectra have also established the low-lying vibrational levels of the ground state. The ground state bending fundamental lies at 660 cm(-1), while the W-C stretching frequency is 1006 cm(-1); the corresponding frequencies in WCD are 501 cm(-1) and 953 cm(-1), respectively. No evidence for the C-H stretching frequency has been found. Emission has also been observed to a low-lying electronic state, 813 cm(-1) above the (X) over tilde 3/2 state. The pattern of rotationally resolved emission to this state clearly indicates that it is a (4) Sigma(1/2) state. Its bending frequency is 612 cm(-1), and its W-C stretching frequency is 971 cm(-1), indicating a slightly longer bond length than in the (X) over tilde 3/2 state. High resolution cw laser spectra of the (0,0) bands of the two lowest excited electronic states [(A) over tilde 3/2((2) Delta) and (B) over tilde 1/2((2) Pi)] reveal a small splitting of the four principal tungsten isotopes (W-182, W-183, W-184, and W-186) which serves to confirm the presence of tungsten in the carrier. Hyperfine splitting associated with the W-183 nucleus (I = 1/2) has been observed for the (0,0) band of the (A) over tilde 3/2- (X) over tilde 3/2 system, allowing the electron configuration of the ground state to be elucidated. (C) 1996 American Institute of Physics.