Band oscillator strengths of the intersystem transitions of CO

Abstract

Absorption oscillator strengths of 18 intersystem bands of CO between 1360 and 1620 Å originating from the ground state and involving the a′ 3Σ+, e 3Σ−, and d 3Δ states have been measured using synchrotron radiation as a background source. They have also been calculated using the published molecular parameters provided by the standard spectroscopic perturbation analysis, including the spin-orbit interaction with the nearby A 1Π state. It was found, however, that the model used in that analysis had to be extended in order to take into account the contributions of several vibrational levels of the A state to the intensity of a given singlet–triplet band. The present measurements are in good agreement with the predictions of this extended model. The puzzling discrepancies reported earlier between oscillator strength or rotationally resolved lifetime measurements and standard calculations are now well understood as well as the temperature variation of some of these band-integrated oscillator strengths. Line and band oscillator strengths of the intercombination transitions can now be reliably predicted at all temperatures and used for the measurement of large CO column densities, especially in interstellar molecular clouds, when the allowed bands normally used are saturated.