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Trial run for importing the nublado.org Trac tickets as GitHub issues
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fast H2 OP conversion on grains (trac #369) #371

Open cloudy-bot opened 8 years ago

cloudy-bot commented 8 years ago

reported by: @CloudyLex

Title:  
Efficient ortho-para conversion of H2 on interstellar grain surfaces
Authors:    
Bron, Emeric; Le Petit, Franck; Le Bourlot, Jacques
Affiliation:    
AA(LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Université Paris 06, 92190, Meudon, France emeric.bron@obspm.fr), AB(LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Université Paris 06, 92190, Meudon, France), AC(LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Université Paris 06, 92190, Meudon, France; Université Paris Diderot, Sorbonne Paris Cité, 75013, Paris, France)
Publication:    
Astronomy & Astrophysics, Volume 588, id.A27, 17 pp. (A&A Homepage)
Publication Date:   
04/2016
Origin: 
EDP Sciences
Astronomy Keywords: 
ISM: molecules, dust, extinction, photon-dominated region (PDR), astrochemistry, molecular processes, methods: numerical
DOI:    
10.1051/0004-6361/201527879
Bibliographic Code: 
2016A&A...588A..27B
Abstract

Context. Fast surface conversion between ortho- and para-H2 has been 
observed in laboratory studies, and it has been proposed that this mechanism 
plays a role in the control of the ortho-para ratio in the interstellar medium. 
Observations of rotational lines of H2 in photo-dissociation regions (PDRs) have 
indeed found significantly lower ortho-para ratios than expected at equilibrium. 
The mechanisms controlling the balance of the ortho-para ratio in the interstellar 
medium thus remain incompletely understood, while this ratio can affect the 
thermodynamical properties of the gas (equation of state, cooling function). 

Aims: We aim to build an accurate model of ortho-para conversion on dust 
surfaces based on the most recent experimental and theoretical results, and to 
validate it by comparison to observations of H2 rotational lines in PDRs. 

Methods: We propose a statistical model of ortho-para conversion on dust grains 
with fluctuating dust temperatures. It is based on a master equation approach. 
This computation is then coupled to full PDR models and compared to PDR 
observations. 

Results: We show that the observations of rotational H2 lines indicate a high 
conversion efficiency on dust grains and that this high efficiency can be 
accounted for if taking dust temperature fluctuations into account with our 
statistical model of surface conversion. Simpler models that neglect the dust 
temperature fluctuations do not reach the high efficiency deduced from the 
observations. Moreover, this high efficiency induced by dust temperature 
fluctuations is very insensitive to the values of the model's microphysical 
parameters. 

Conclusions: Ortho-para conversion on grains is thus an efficient mechanism in 
most astrophysical conditions and can play a significant role in controlling the 
ortho-para ratio.

Migrated from https://www.nublado.org/ticket/369

{
    "status": "new",
    "changetime": "2019-02-04T13:02:49Z",
    "_ts": "1549285369825011",
    "description": "{{{\nTitle:\t\nEfficient ortho-para conversion of H2 on interstellar grain surfaces\nAuthors:\t\nBron, Emeric; Le Petit, Franck; Le Bourlot, Jacques\nAffiliation:\t\nAA(LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universit\u00e9s, UPMC Universit\u00e9 Paris 06, 92190, Meudon, France emeric.bron@obspm.fr), AB(LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universit\u00e9s, UPMC Universit\u00e9 Paris 06, 92190, Meudon, France), AC(LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universit\u00e9s, UPMC Universit\u00e9 Paris 06, 92190, Meudon, France; Universit\u00e9 Paris Diderot, Sorbonne Paris Cit\u00e9, 75013, Paris, France)\nPublication:\t\nAstronomy & Astrophysics, Volume 588, id.A27, 17 pp. (A&A Homepage)\nPublication Date:\t\n04/2016\nOrigin:\t\nEDP Sciences\nAstronomy Keywords:\t\nISM: molecules, dust, extinction, photon-dominated region (PDR), astrochemistry, molecular processes, methods: numerical\nDOI:\t\n10.1051/0004-6361/201527879\nBibliographic Code:\t\n2016A&A...588A..27B\nAbstract\n\nContext. Fast surface conversion between ortho- and para-H2 has been \nobserved in laboratory studies, and it has been proposed that this mechanism \nplays a role in the control of the ortho-para ratio in the interstellar medium. \nObservations of rotational lines of H2 in photo-dissociation regions (PDRs) have \nindeed found significantly lower ortho-para ratios than expected at equilibrium. \nThe mechanisms controlling the balance of the ortho-para ratio in the interstellar \nmedium thus remain incompletely understood, while this ratio can affect the \nthermodynamical properties of the gas (equation of state, cooling function). \n\nAims: We aim to build an accurate model of ortho-para conversion on dust \nsurfaces based on the most recent experimental and theoretical results, and to \nvalidate it by comparison to observations of H2 rotational lines in PDRs. \n\nMethods: We propose a statistical model of ortho-para conversion on dust grains \nwith fluctuating dust temperatures. It is based on a master equation approach. \nThis computation is then coupled to full PDR models and compared to PDR \nobservations. \n\nResults: We show that the observations of rotational H2 lines indicate a high \nconversion efficiency on dust grains and that this high efficiency can be \naccounted for if taking dust temperature fluctuations into account with our \nstatistical model of surface conversion. Simpler models that neglect the dust \ntemperature fluctuations do not reach the high efficiency deduced from the \nobservations. Moreover, this high efficiency induced by dust temperature \nfluctuations is very insensitive to the values of the model's microphysical \nparameters. \n\nConclusions: Ortho-para conversion on grains is thus an efficient mechanism in \nmost astrophysical conditions and can play a significant role in controlling the \northo-para ratio.\n\n}}}",
    "reporter": "gary",
    "cc": "",
    "resolution": "",
    "time": "2016-09-02T22:10:23Z",
    "component": "atomic/molecular data base",
    "summary": "fast H2 OP conversion on grains",
    "priority": "good to do",
    "keywords": "",
    "version": "trunk",
    "milestone": "no milestone",
    "owner": "nobody",
    "type": "enhancement"
}
cloudy-bot commented 8 years ago

@peter-van-hoof-noaccount changed milestone from "" to "no milestone"