H2 reformation in post-shock regions

Abstract

H2 formation is an important process in post-shock regions, since H2 is an active participant in the cooling and shielding of the environment. The onset of H2 formation therefore has a strong effect on the temperature and chemical evolution in the post shock regions. We recently developed a model for H2 formation on a graphite surface in warm conditions. The graphite surface acts as a model system for grains containing large areas of polycyclic aromatic hydrocarbon structures. Here this model is used to obtain a new description of the H2 formation rate as a function of gas temperature that can be implemented in molecular shock models. The H2 formation rate is substantially higher at high gas temperatures as compared to the original implementation of this rate in shock models, because of the introduction of H atoms which are chemically bonded to the grain (chemisorption). Since H2 plays such a key role in the cooling, the increased rate is found to have a substantial effect on the predicted line fluxes of an important coolant in dissociative shocks [O I] at 63.2 and 145.5 micron. With the new model a better agreement between model and observations is obtained. Since one of the goals of Herschel/PACS will be to observe these lines with higher spatial resolution and sensitivity than the former observations by ISO-LWS, this more accurate model is very timely to help with the interpretation of these future results.

12 pages, 3 figures, 1 table, accepted in MNRAS Letters

References in corpus (4)

• Kinetic Monte Carlo Studies of Hydrogen Abstraction from Graphite
• Molecular line emission in HH54: a coherent view from near to far infrared
• IR diagnostics of embedded jets: kinematics and physical characteristics of the HH46-47 jet
• A kinetic Monte Carlo study of desorption of H2 from graphite (0001)

Cited by in corpus (15)

• The warm gas atmosphere of the HD 100546 disk seen by Herschel (Evidence of a gas-rich, carbon-poor atmosphere?)
• The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime
• Surface chemistry in the interstellar medium - I - H2 formation by Langmuir-Hinshelwood and Eley-Rideal mechanisms
• Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220
• Water ice deuteration: a tracer of the chemical history of protostars
• Formation of Organic Molecules and Water in Warm Disk Atmospheres
• Interstellar H${}_2$O Masers from J Shocks
• Efficiency of non-thermal desorptions in cold-core conditions. Testing the sputtering of grain mantles induced by cosmic rays
• Sticking coefficient of hydrogen and deuterium on silicates under interstellar conditions
• Why does ammonia not freeze out in the center of pre-stellar cores?
• The redshift evolution of major merger triggering of luminous AGN: a slight enhancement at z$\sim$2
• Nearby early-type galaxies with ionized gas VI. The Spitzer-IRS view
• When sticking influences H2 formation
• Complex organic molecules along the accretion flow in isolated and externally irradiated protoplanetary disks
• Enhanced H2O formation through dust grain chemistry in X-ray exposed environments