Vibrationally Excited H 2, HCl, and NO + in the Diffuse Clouds toward zeta Ophiuchi
van Dishoeck, Ewine F.; Federman, S. R.; Lambert, David L.; Black, J. H.; Cardell, Jason A.
United States, Netherlands
Abstract
Absorption lines from vibrationally excited H2 and from HCl were detected in the ultraviolet spectrum of Zeta Oph with the Hubble Space Telescope (HST). Improved upper limits on NO(+) absorption were obtained as well. The data were analyzed with an updated version of a chemical model for diffuse clouds (van Dishoeck & Black 1986) as a guide to understanding this gaseous environment. The comparisons suggest that the flux of ultraviolet radiation impinging on the cloud surface is approximately 1-2 times the average interstellar radiation field, which is lower than once believed.