Book contents
- Frontmatter
- Contents
- Preface
- Conference participants
- Conference photograph / poster
- 1 Physics of H2 and HD
- 2 Formation - Destruction
- 3 Observations and Models
- Non Stationary C-shocks: H2 Emission in Molecular Outflows
- The Ortho/Para Ratio in C and J-type Shocks
- Theoretical Models of Photodissociation Fronts
- ISO Spectroscopy of H2 in Star Forming Regions
- Observations of the H2 Ortho-Para Ratio in Photodissociation Regions
- H2 Emission from CRL618
- Hydrogen in Photodissociation Regions: NGC2023 and NGC7023
- A Pre-FUSE View of H2
- H2 Absorption Line Measurements with ORFEUS
- Ultraviolet Observations of Molecular Hydrogen in Interstellar Space
- FUSE and Deuterated Molecular Hydrogen
- ISO-SWS Observations of H2 in Galactic Sources
- H2 in Molecular Supernova Remnants
- 3D Integral Field H2 Spectroscopy in Outflows
- Near-Infrared Imaging and [OI] Spectroscopy of IC443 using 2MASS and ISO
- ISOCAM Spectro-imaging of the Supernova Remnant IC443
- Spatial Structure of a Photo-Dissociation Region in Ophiucus
- Tracing H2 Via Infrared Dust Extinction
- The Small Scale Structure of H2 Clouds
- Hot Chemistry in the Cold Diffuse Medium: Spectral Signature in the H2 Rotational Lines
- H2 Observations of the OMC-1 Outflow with the ISO-SWS
- 4 Extragalactic and Cosmology
- 5 Outlook
- Author index
Hot Chemistry in the Cold Diffuse Medium: Spectral Signature in the H2 Rotational Lines
from 3 - Observations and Models
Published online by Cambridge University Press: 04 August 2010
- Frontmatter
- Contents
- Preface
- Conference participants
- Conference photograph / poster
- 1 Physics of H2 and HD
- 2 Formation - Destruction
- 3 Observations and Models
- Non Stationary C-shocks: H2 Emission in Molecular Outflows
- The Ortho/Para Ratio in C and J-type Shocks
- Theoretical Models of Photodissociation Fronts
- ISO Spectroscopy of H2 in Star Forming Regions
- Observations of the H2 Ortho-Para Ratio in Photodissociation Regions
- H2 Emission from CRL618
- Hydrogen in Photodissociation Regions: NGC2023 and NGC7023
- A Pre-FUSE View of H2
- H2 Absorption Line Measurements with ORFEUS
- Ultraviolet Observations of Molecular Hydrogen in Interstellar Space
- FUSE and Deuterated Molecular Hydrogen
- ISO-SWS Observations of H2 in Galactic Sources
- H2 in Molecular Supernova Remnants
- 3D Integral Field H2 Spectroscopy in Outflows
- Near-Infrared Imaging and [OI] Spectroscopy of IC443 using 2MASS and ISO
- ISOCAM Spectro-imaging of the Supernova Remnant IC443
- Spatial Structure of a Photo-Dissociation Region in Ophiucus
- Tracing H2 Via Infrared Dust Extinction
- The Small Scale Structure of H2 Clouds
- Hot Chemistry in the Cold Diffuse Medium: Spectral Signature in the H2 Rotational Lines
- H2 Observations of the OMC-1 Outflow with the ISO-SWS
- 4 Extragalactic and Cosmology
- 5 Outlook
- Author index
Summary
Most of the diffuse interstellar medium is cold, but it must harbor pockets of hot gas to explain the large observed abundances of molecules like CH+, OH and HCO+. Because they dissipate locally large amounts of kinetic energy, MHD shocks and coherent vortices in turbulence can drive endothermic chemical reactions or reactions with large activation barriers. We predict the spectroscopic signatures in the H2 rotational lines of MHD shocks and vortices and compare them to those observed with the ISO-SWS along a line of sight through the Galaxy which samples 20 magnitudes of mostly diffuse gas.
The trigger of hot chemistry in the cold diffuse medium
The large observed abundances of CH, CH+, HCO+, and OH in the (mainly cold) diffuse medium (T ≈ 50 K) imply that activation barriers and endothermicities of several 103 K are overcome. Pockets of hot gas must therefore exist. Large ion-neutral drift speeds, of several km s−1, can equally contribute to triggering certain ion-neutral reactions in cold gas, such as the endothermic reaction C+ + H2 which forms CH+ (ΔE/k=4640 K). Two phenomena, operating at very different scales, are able to reproduce the observed abundances. These are MHD shocks (Flower & Pineau des Forêts, 1998 and references therein) and intense vortices, thought to be responsible for a large fraction of the viscous dissipation of supersonic turbulence (Joulain et al. 1998).
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- Molecular Hydrogen in Space , pp. 225 - 230Publisher: Cambridge University PressPrint publication year: 2000
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