Title:
H2 formation on PAHs in photodissociation regions: a high-temperature pathway to molecular hydrogen
Authors:
Boschman, L.; Cazaux, S.; Spaans, M.; Hoekstra, R.; Schlathölter, T.
Aims: Molecular hydrogen is the most abundant molecule in the Universe. It is
thought that a large portion of H2 forms by association of hydrogen atoms to
polycyclic aromatic hydrocarbons (PAHs). We model the influence of PAHs on
total H2 formation rates in photodissociation regions (PDRs) and assess the
effect of these formation rates on the total cloud structure.
Methods: We set up a chemical kinetic model at steady state in a PDR
environment and included radiative transfer to calculate the chemistry at
different depths in the PDR. This model includes known dust grain chemistry for
the formation of H2 and a H2 formation mechanism on PAHs. Since H2
formation on PAHs is impeded by thermal barriers, this pathway is only efficient
at higher temperatures (T> 200 K). At these temperatures the conventional route
of H2 formation via H atoms physisorbed on dust grains is no longer feasible,
so the PAH mechanism enlarges the region where H2 formation is possible.
Results: We find that PAHs have a significant influence on the structure of
PDRs. The extinction at which the transition from atomic to molecular hydrogen
occurs strongly depends on the presence of PAHs, especially for PDRs with a
strong external radiation field. A sharp spatial transition between fully
dehydrogenated PAHs on the outside of the cloud and normally hydrogenated
PAHs on the inside is found. As a proof of concept, we use coronene to show
that H2 forms very efficiently on PAHs, and that this process can reproduce the
high H2 formation rates derived in several PDRs.
{
"status": "new",
"changetime": "2019-02-04T13:07:06Z",
"_ts": "1549285626580696",
"description": "http://adsabs.harvard.edu/abs/2015A%26A...579A..72B\n\n2015A&A...579A..72B\n\n{{{\nTitle:\t\nH2 formation on PAHs in photodissociation regions: a high-temperature pathway to molecular hydrogen\nAuthors:\t\nBoschman, L.; Cazaux, S.; Spaans, M.; Hoekstra, R.; Schlath\u00f6lter, T.\n\nAims: Molecular hydrogen is the most abundant molecule in the Universe. It is \nthought that a large portion of H2 forms by association of hydrogen atoms to \npolycyclic aromatic hydrocarbons (PAHs). We model the influence of PAHs on \ntotal H2 formation rates in photodissociation regions (PDRs) and assess the \neffect of these formation rates on the total cloud structure. \n\nMethods: We set up a chemical kinetic model at steady state in a PDR \nenvironment and included radiative transfer to calculate the chemistry at \ndifferent depths in the PDR. This model includes known dust grain chemistry for \nthe formation of H2 and a H2 formation mechanism on PAHs. Since H2 \nformation on PAHs is impeded by thermal barriers, this pathway is only efficient \nat higher temperatures (T> 200 K). At these temperatures the conventional route \nof H2 formation via H atoms physisorbed on dust grains is no longer feasible, \nso the PAH mechanism enlarges the region where H2 formation is possible. \n\nResults: We find that PAHs have a significant influence on the structure of \nPDRs. The extinction at which the transition from atomic to molecular hydrogen \noccurs strongly depends on the presence of PAHs, especially for PDRs with a \nstrong external radiation field. A sharp spatial transition between fully \ndehydrogenated PAHs on the outside of the cloud and normally hydrogenated \nPAHs on the inside is found. As a proof of concept, we use coronene to show \nthat H2 forms very efficiently on PAHs, and that this process can reproduce the \nhigh H2 formation rates derived in several PDRs.\n\n}}}\n",
"reporter": "gary",
"cc": "",
"resolution": "",
"time": "2015-07-12T21:47:38Z",
"component": "chemical network",
"summary": "H2 formation on PAHs",
"priority": "major",
"keywords": "",
"version": "trunk",
"milestone": "no milestone",
"owner": "nobody",
"type": "enhancement"
}
reported by: @CloudyLex
http://adsabs.harvard.edu/abs/2015A%26A...579A..72B
2015A&A...579A..72B
Migrated from https://www.nublado.org/ticket/336