THE NEAR-INFRARED ELECTRONIC-SPECTRUM OF TUNGSTEN METHYLIDYNE, WCH

The laser excitation spectrum of tungsten methylidyne, WCH, has been r ecorded in the 12 000-15 400 cm(-1) region. A total of 14 vibronic ban ds of WCH and 16 bands of WCD have been observed in this region. Rotat ional analysis shows that the ground state is (X) over tilde 3/2((2) D elta), with the substitution structure r(0)(W=C)=1.7366(5) Angstrom an d r(0)(C-H)=1.076(5) Angstrom. The excited vibronic levels have been a ssigned, on the basis of their WCH/WCD isotope shifts and their wavele ngth resolved fluorescence patterns, to three electronic states, (A) o ver tilde 3/2((2) Delta), (B) over tilde 1/2((2) Pi), and (C) over til de 5/2(2 Phi), at 12 090, 13 392, and 14 110 cm(-1), respectively. The wavelength resolved fluorescence spectra have also established the lo w-lying vibrational levels of the ground state. The ground state bendi ng 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) an d 953 cm(-1), respectively. No evidence for the C-H stretching frequen cy has been found. Emission has also been observed to a low-lying elec tronic state, 813 cm(-1) above the (X) over tilde 3/2 state. The patte rn of rotationally resolved emission to this state clearly indicates t hat 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 resolut ion cw laser spectra of the (0,0) bands of the two lowest excited elec tronic 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 isotope s (W-182, W-183, W-184, and W-186) which serves to confirm the presenc e 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 con figuration of the ground state to be elucidated. (C) 1996 American Ins titute of Physics.