FUSE Measurements of Rydberg Bands of Interstellar CO between 925 and 1150 Å

We report the detection of 11 Rydberg bands of CO in FUSE spectra of the sight line toward HD203374A. Eight of these electronic bands are seen in the interstellar medium for the first time. Our simultaneous fit of five non-Rydberg A−X bands together with the strongest Rydberg band of CO, C−X (0−0), yields a 4-component cloud structure toward the stellar target. With this model we synthesize the other Rydberg bands in order to derive their oscillator strengths. We find that the strength of some bands was underestimated in previously published results from laboratory measurements. The implication is important for theoretical calculations of the abundance of interstellar CO, because its dissociation and self shielding depend on oscillator strengths for these bands.