Band oscillator strengths of the intersystem transitions of CO

Absorption oscillator strengths of 18 intersystem bands of CO between 1360 and 1620 Angstrom originating from the ground state and involving the a(') (3)Sigma(+), e (3)Sigma(-), and d (3)Delta states have been measured using synchrotron radiation as a background source. They have also been calculate d using the published molecular parameters provided by the standard spectro scopic perturbation analysis, including the spin-orbit interaction with the nearby A (1)Pi state. It was found, however, that the model used in that a nalysis 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 si nglet-triplet band. The present measurements are in good agreement with the predictions of this extended model. The puzzling discrepancies reported ea rlier between oscillator strength or rotationally resolved lifetime measure ments and standard calculations are now well understood as well as the temp erature variation of some of these band-integrated oscillator strengths. Li ne and band oscillator strengths of the intercombination transitions can no w be reliably predicted at all temperatures and used for the measurement of large CO column densities, especially in interstellar molecular clouds, wh en the allowed bands normally used are saturated. (C) 2000 American Institu te of Physics. [S0021-9606(00)01102-8].