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 ?'e8(184W12C)=752.6(4.9) cm-1 and a bond length of r'e8(184W12C)=1.747(4) ?. Several unassigned bands were also rotationally resolved and analyzed. All of the observed bands are ?'=2??"=1 transitions, confirming the predicted ground state of 3?1 arising from a 14??8rr?15??4?116?1 configuration. The measured line positions in these bands were simultaneously fitted to provide B"=0.509 66(10) cm-1 for 184W12C, corresponding to r"0(184W12C)=1.713 5(2) ?. 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 ?e=983(4) cm-1 and ?exe=11(1) cm-1, and have also permitted the low-lying [1.2] 3?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.