2001/10/30 by Benjamin J. McCall, B. J. McCall, K. H. Hinkle +13 · 7 citations
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Analytical Chemistry (journal) #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Atomic physics #Chemistry #Crystallography #Electron #Electron density #Infrared #Infrared spectroscopy #Ion #Ionization #Molecular Spectroscopy and Structure #Optics #Physics #Quantum mechanics #astro-ph
paper · pdf · doi:10.1086/338380
To be published in Astrophysical Journal, March 2002
arxiv created 2001/10/30 · openalex publication_date 2002/03/01 · arxiv updated 2009/12/01 · openalex created_date 2022/08/26 · openalex updated_date 2026/08/01
Surprisingly large column densities of H have been detected using infrared absorption spectroscopy in seven diffuse cloud sight lines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating that H is ubiquitous in the diffuse interstellar medium. Using the standard model of diffuse cloud chemistry, our H column densities imply unreasonably long path lengths (~1 kpc) and low densities (~3 cm -3 ). Complimentary millimeter-wave, infrared, and visible observations of related species suggest that the chemical model is incorrect and that the number density of H must be increased by 1-2 orders of magnitude. Possible solutions include a reduced electron fraction, an enhanced rate of H 2 ionization, and/or a smaller value of the H dissociative recombination rate constant than implied by laboratory experiments.