Predissociation of the 4p pi L-1 Pi Rydberg state of carbon monoxide

Time-domain and frequency-domain spectroscopic experiments have been performed on the (4ppi)L(1)Pi, v = 0 Rydberg state in three isotopomers of carbon monoxide. Accurate values for the excited state lifetimes of the f-parity components have been determined: tau((CO)-C-12-O-16) = 1.08 +/- 0.05 ns, tau((CO)-C-13-O-16) = 72 +/- 10 ps and tau((CO)-C-13-O-18) = 29 +/- 6 ps. The spectral resolution in the frequency-domain experiment goes as far as the limit imposed by the natural lifetime; Q-branch lines, or f-parity components of the heavier isotopes, are resolved for the first time. Highly accurate transition frequencies are determined in a molecular beam experiment using comparison and interpolation with a saturated iodine reference standard. The results reveal a number of perturbations and predissociation mechanisms, displaying a high degree of complexity in the energetic region of the 4p Rydberg states of CO with strong isotopic effects. (C) 2002 Elsevier Science B.V. All rights reserved.