Predissociation in the E 1Π, v=1 state of the six natural isotopomers of CO

The E (1)Pi, upsilon = 1 state of carbon monoxide is studied in high resolution using a tunable and narrowband laser source in the vacuum ultraviolet near 105 nm. Calibration with respect to a reference standard consisting of iodine lines in the visible range, measured by saturated absorption spectroscopy, yields an absolute accuracy of 0.003 cm(-1) for the CO resonances. Transition frequencies of the E-X(1,0) band were determined for all six natural isotopomers ((CO)-C-12-O-16, (CO)-C-12-O-17, (CO)-C-12-O-18, (CO)-C-13-O-16, (CO)-C-13-O-17, and (CO)-C-13-O-18) and improved molecular constants derived. Natural lifetime broadening, caused by predissociation was investigated quantitatively for single rotational and (e)-(f ) parity levels. The accidental predissociation phenomena, giving rise to line shifts and broadening, could be explained up to the experimental accuracy in a model based on spin-orbit-coupling between E (1)Pi, upsilon = 1 and k (3)Pi, upsilon = 6 states, with a coupling constant of H-E,H-k = 1.88 +/- 0.01 cm(-1) for all six isotopomers. The overall line broadening parameter Gamma(E) for the E state, ascribed to interaction with a repulsive (1)Pi state, and Gamma(k) for the k state, were determined as well; the predissociation rates were found to decrease with increasing reduced mass of the isotopomers for both E (1)Pi, upsilon = 1 and k (3)Pi, upsilon = 6 states. (C) 2000 American Institute of Physics. [S0021-9606(00)00726-1].