Ortho to para conversion of H2 on interstellar grains
J. Le Bourlot
Received 28 April 2000 / Accepted 15 June 2000
Fast conversion of ortho- to para- can occur (and has been observed in the laboratory) on the surface of non magnetic, non metallic grains. In a PDR, the fraction of converted depends on the ratio of the characteristic time of conversion (of the order of 1 minute) to the residence time of physisorbed . This later time is itself an exponentially varying function of the grain temperature and of the adsorption binding energy of . Conversion is very efficient in cool PDRs if the dust temperature is below a critical temperature that we determine, and leads to a much reduced ortho to para ratio of in the gas phase. Emission lines within para levels of are significantly enhanced.
Key words: molecular processes ISM: molecules ISM: abundances ISM: dust, extinction
Send offprint requests to: J. Le Bourlot
Correspondence to: Jacques.Lebourlot@obspm.fr
This article contains no SIMBAD objects.
© European Southern Observatory (ESO) 2000
Online publication: August 17, 2000