THE INTERSTELLAR ABUNDANCE OF THE HYDROGEN MOLECULE: I. BASIC PROCESSES,
Abstract
An analysis is given of the various processes which determine the molecular concentration in H I cloudshe most important mechanism for forming molecular hydrogen is association on the surface of the interstellar grains, the characteristic time for conversion to molecular form being about 100 million years. It is shown that the range of grain temperatures where this recombination reaction is efficient is coincident with the range 5-20 K which is expected to result from the interaction with the interstellar radiation field. It is estimated that the efficiency (recombination coefficient) of the process is between 0.1 and 1. Regarding dissociative processes, photodissociation through the forbidden transition between the two Heitler London states of the molecule, previously thought to be most important, is shown to be negligible. Ionization and dissociation of a cloud by random encounters with O and B stars occurs about once every 100 million years, so that if the grain recombination process is operative a balance results in which the molecular abundance is roughly comparable to the observed atomic concentration. The cooling properties of molecular hydrogen are discussed. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1963
- Accession Number
- AD0413840
Entities
People
- Edwin E. Salpeter
- Robert J. Gould
Organizations
- Cornell University