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

Abstract

The E 1Π, v=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 (12C16O, C1712O, C1812O, C1613O, C1713O, and C1813O) 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 1Π, v=1 and k 3Π, v=6 states, with a coupling constant of HE,k=1.88±0.01 cm−1 for all six isotopomers. The overall line broadening parameter ΓE for the E state, ascribed to interaction with a repulsive Π1 state, and Γk 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 1Π, v=1 and k 3Π, v=6 states.