Journal of Chemical Physics, Vol.116, No.3, 993-1002, 2002
Optical spectroscopy of tungsten carbide (WC)
Resonant two-photon ionization spectroscopy has been used to study the diatomic transition-metal carbide, WC. A low-resolution scan revealed a five-member vibrational progression beginning with the 0-0 band at 17 585 cm(-1). Analysis of this progression yielded a vibrational frequency of omega (')(e)((WC)-W-184-C-12)=752.6(4.9) cm(-1) and a bond length of r(e)(')((WC)-W-184-C-12)=1.747(4) Angstrom. Several unassigned bands were also rotationally resolved and analyzed. All of the observed bands are Omega'=2 <-- Omega'=1 transitions, confirming the predicted ground state of (3)Delta (1) arising from a 14 sigma (2)8 pi (4)15 sigma (2)4 delta (1)16 sigma (1) configuration. The measured line positions in these bands were simultaneously fitted to provide B-0(')=0.509 66(10) cm(-1) for (WC)-W-184-C-12, corresponding to r(0)(')((WC)-W-184-C-12)=1.713 5(2) Angstrom. These values are corrected for spin-uncoupling effects in the ground state and represent our best estimate of the true bond length of WC. Dispersed fluorescence studies provide the ground-state vibrational constants of omega (e)=983(4) cm(-1) and omega (e)x(e)=11(1) cm(-1), and have also permitted the low-lying [1.2] (3)Delta (2) and [4.75] states to be located and characterized. These results on WC are discussed in relation to the isovalent molecule MoC and other transition-metal carbides.