Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...324..221m&link_type=abstract
Astronomy and Astrophysics, v.324, p.221-236
Astronomy and Astrophysics
Astrophysics
15
Molecular Processes, Ism: Abundances, Molecules, Radio Lines: Ism
Scientific paper
Molecular oxygen has not yet been observed in interstellar clouds because of the opacity of the Earth's atmosphere. Due to its potential importance in interstellar chemistry, several projets attempting to detect rotational lines of O_2_ are being developed using millimeter and submillimeter receivers embarked on satellites or stratospheric balloons: ODIN for the 119 and 487GHz lines, SWAS for the 487GHz line, PRONAOS-SMH for the 368GHz line and PIROG 8 for the 425GHz line. As a theoretical preparation to these projects and taking advantage of recent developments in interstellar chemistry as well as recent cross-section calculations of collisional excitation of O_2_, we have used an interstellar cloud model to perform a non-LTE calculation of O_2_ rotational population. O_2_ column densities and emissivities of its rotational lines at (sub)millimeter wavelengths are predicted for various conditions in diffuse, translucent and dense dark clouds, covering a range of visual extinction from 1 to 30. The effects of density, temperature, external ultraviolet radiation field and gas phase elemental abundances on the O_2_ abundance and rotational excitation have been investigated. Our results are confronted to the ones obtained by Black & Smith (1984) who adressed initially the problem of the detectability of interstellar O_2_. If density and temperature have little influence on the O_2_ abundance, it is not the case for the UV radiation field which efficiently destroys O_2_ so as to prevent its detection in most clouds as soon as it is enhanced by a factor of 1000 with respect to the local standard value. The most drastic parameter that influences the abundance of O_2_ -- as well as that of OH and H_2_O -- is the gas-phase C/O abundance ratio: for C/O ratio larger than 0.7, O_2_ becomes unobservable by all forthcoming missions except for the 119GHz line which remains observable in very opaque clouds (A_V_ ~ 20) up to C/O = 1. The rate coefficient of the reaction O+OH->O_2_+H which produces molecular oxygen has little influence on the O_2_ abundance in clouds sufficiently opaque to allow detection; it however controls the OH abundance since it is the main destruction process of this molecule. Our model calculations also predict that the radiative de-excitation of O_2_ rotational levels could be an important cooling agent in cold molecular clouds with an efficiency comparable to that of CO.
Benayoun Jean-Jacques
Maréchal Pierre
Viala Y. P.
No associations
LandOfFree
Chemistry and rotational excitation of O_2_ in interstellar clouds. I. Predicted emissivities of lines for the ODIN, SWAS, PRONAOS-SMH and PIROG 8 submillimeter receivers. does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Chemistry and rotational excitation of O_2_ in interstellar clouds. I. Predicted emissivities of lines for the ODIN, SWAS, PRONAOS-SMH and PIROG 8 submillimeter receivers., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chemistry and rotational excitation of O_2_ in interstellar clouds. I. Predicted emissivities of lines for the ODIN, SWAS, PRONAOS-SMH and PIROG 8 submillimeter receivers. will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1877611