Hubble Space Telescope Measurements of Vacuum Ultraviolet Lines of Interstellar Ch

Three interstellar absorption lines near 13708 seen toward Oph have been assigned byWatson to Rydberg transitions in theGYX (or 3dYX ) band of CH. Our survey of a dozen diffuse interstellar lines of sight shows that the three absorption lines are consistent with the known column densities of CH, by deriving the following oscillator strengths: f (1368:74) 1⁄4 0:019 0:003, f (1369:13) 1⁄4 0:030 0:005, and f (1370:87) 1⁄4 0:009 0:001.We also determined intrinsic linewidths that correspond to decay rates of (1:5 0:6) ; 10, (3:8 0:7) ; 10, and (1:1 0:6) ; 10 s 1 for kk1368, 1369, and 1370, respectively. These rates are significantly higher than those associated with radiative decays and, thus, are readily attributable to predissociation of the Rydberg state. A fourth interstellar line near 12718 has been conjectured byWatson to be the strongest transition in the 4dYX Rydberg band of CH. We detected this line along four sight lines and our spectrum syntheses show that with f (1271:02) 1⁄4 0:007 0:002, it is also consistent with the known column densities of CH. In addition, we conducted a search for theFYX band of CH near 15498, and successfully discovered two of its absorption features along four sight lines. The astronomical oscillator strengths derived for these features are f (1549:05) 1⁄4 0:021 0:006 and f (1549:62) 1⁄4 0:013 0:003. Finally, the X Per sight line provided us with an astronomical detection of another CH band via twoDYX features near 16948. Comparisons with results of available theoretical calculations for the four CH bands are presented. Subject headings: ISM: lines and bands — ISM: molecules — molecular data — ultraviolet: ISM