NICHOLAS INDRIOLO, BENJAMIN J. MCCALL, Department of Astronomy and Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801; THOMAS R. GEBALLE, Gemini Observatory, Hilo, HI 96720; TAKESHI OKA, Department of Astronomy & Astrophysics and Department of Chemistry, University of Chicago, Chicago, IL 60637.
\hspace0.25in In the past several years H3+ has been detected in diffuse interstellar clouds where it had been predicted to exist in abundances below observable limits. These detections led to several questions about H3+ chemistry and the diffuse cloud environment. To answer these questions, further studies of H3+ were performed to constrain some uncertain parameters such as the electron recombination rate constant. With new data and some reasonable assumptions it became possible to infer the cosmic-ray ionization rate necessary to produce column densities of H3+ observed by the CGS4 spectrometer on the United Kingdom Infrared Telescope (UKIRT). However, the value calculated along the sightline to Per was over an order of magnitude higher than the value found in previous studies using OH,.
\hspace0.25in Recently, we finished analyzing a survey of H3+ in twenty diffuse cloud sightlines. In total, eight of these sightlines yielded positive detections of H3+ with another one or two hinting at possible absorption. Using the observed column densities, we calculated the primary cosmic-ray ionization rate and found an average value of p~2×10-16 sec-1. This is about an order of magnitude larger than what has long been considered the canonical ionization rate. Taking this higher ionization rate into account, some newer models have been proposed to explain both the H3+ column densities, as well as the abundances of other species. The observation of H3+ along many diffuse cloud sightlines, coupled with the lack of a clear correlation between position and ionization rate, suggests that an enhanced cosmic-ray ionization rate may be a general property of the diffuse interstellar medium.