Oscillator Strengths for B – X , C – X , and E – X Transitions in Carbon Monoxide

Abstract

Band oscillator strengths for electronic transitions in CO were obtained at the Synchrotron Radiation Center of the University of Wisconsin-Madison. Our focus was on transitions observed in interstellar spectra with the Far-Ultraviolet Spectroscopic Explorer; these transitions are also important in studies of selective isotope photodissociation, where fractionation among isotopomers can occur. Absorption from the ground state X 1Σ+ (v'' = 0) to A 1Π (v' = 5), B 1Σ+ (v' = 0, 1), C 1Σ+ (v' = 0, 1), and E 1Π (v' = 0) was measured. Fits to the A-X (5, 0) band, whose oscillator strength is well known, yielded the necessary column density and excitation temperature. These parameters were used in a least-squares fit of the observed profiles to extract the band oscillator strengths of the transitions of interest. Our oscillator strengths are in excellent agreement with results from recent experiments using a variety of techniques. This agreement provides the basis for a self-consistent set of f-values at far-ultraviolet wavelengths for studies of interstellar (and stellar) CO.