Fourier transform microwave spectrum of and Born-Oppenheimer breakdown effects in tungsten monoxide, WO

Rotational transitions of eight isotopomers of tungsten monoxide, WO, in its X0(+) ground electronic state, have been measured in the frequency range 22-26 GHz, using a cavity Fourier transform microwave spectrometer. The samples were prepared by laser ablation of W metal in the presence of O-2 and stabilized in pulsed supersonic jets of Ne or Ar. Only the J = 1-0 transition was accessible within the frequency range of the spectrometer. It was measured for the ground (nu = 0) and two excited (nu = 1, 2) vibrational states. Hyperfine structure due to W-183 nuclear spin-rotation coupling was found for (WO)-W-183. The overall spectral fit used a Dunham-type expression including Born-Oppenheimer breakdown parameters. Only the nu = 0 and 1 states could be fit to the measurement accuracy because of a small perturbation of the nu = 2 state. It was necessary to account for the finite nuclear size of the W nucleus in the fit. The resulting parameter V-01(W) agreed well with a value calculated using density functional theory. Equilibrium internuclear distances re have been evaluated.