J/A+A/472/1029 (De)excitation rates of H2O by H2 (Faure+, 2007)
Quasi-classical rate coefficient calculations for the rotational
(de)excitation of H2O by H2.
Faure A., Crimier N., Ceccarelli C., Valiron P., Wiesenfeld L., Dubernet L.
<Astron. Astrophys. 472, 1029 (2007)>
=2007A&A...472.1029F 2007A&A...472.1029F
ADC_Keywords: Atomic physics
Keywords: molecular data ; molecular processes ; ISM: molecules
Abstract:
The interpretation of water line emission from existing observations
and future HIFI/Herschel data requires a detailed knowledge of
collisional rate coefficients. Among all relevant collisional
mechanisms, the rotational (de)excitation of H2O by H2 molecules is
the process of most interest in interstellar space. We provide rate
coefficients for rotational de-excitation among the lowest 45 para and
45 ortho rotational levels of H2O colliding with both para and
ortho-H2 in the temperature range 20-2000K. Rate coefficients are
calculated on a recent high-accuracy H2O-H2 potential energy surface
using quasi-classical trajectory calculations. Trajectories are
sampled by a canonical Monte-Carlo procedure. H2 molecules are assumed
rotationally thermalized at the kinetic temperature. By comparison
with quantum calculations available for low lying levels, classical
rates are found to be accurate within a factor of 1-3 for the dominant
transitions, that is those with rates larger than a few
10-12cm3/s. Large velocity gradient modelling shows that the new
rates have a significant impact on emission line fluxes and that they
should be adopted in any detailed population model of water in warm
and hot environments.
Description:
For each of the 4 spin symmetries and 8 temperatures, 990 *downward*
rotational rates are provided, corresponding to all possible
transitions among 45 levels. Upward rates can be computed using the
detailed balance relation (see article).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
oh2olev.dat 53 45 Rotational energy levels of ortho-H2O in its
ground vibrational state
ph2olev.dat 53 45 Rotational energy levels of para-H2O in its
ground vibrational state
oh2ooh2.dat 80 990 De-excitation rates of ortho-H2O in collision
with ortho-H2
oh2oph2.dat 80 990 De-excitation rates of ortho-H2O in collision
with para-H2
ph2ooh2.dat 80 990 De-excitation rates of para-H2O in collision
with ortho-H2
ph2oph2.dat 80 990 *De-excitation rates of para-H2O in collision
with para-H2
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Note on ph2oph2.dat : The labelling of para-H2O levels (i and f stand for
initial and final) is taken from Green et al. (1993ApJS...85..181G 1993ApJS...85..181G).
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See also:
J/A+A/492/257 : Collisional excitation of water in warm media (Faure+, 2008)
J/A+A/493/687 : Rotational excitation of formaldehyde by H2 (Faure+, 2009)
J/MNRAS/399/425 : (De)excitation rates of ortho-NH3 and para-NH3 (Faure+, 2009)
Byte-by-byte Description of file(%): oh2olev.dat ph2olev.dat
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Bytes Format Units Label Explanations
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7- 8 I2 --- Level [1/45] Level
13- 23 F11.6 cm-1 E Energy
32- 33 I2 --- J J quantum number
43 I1 --- Ka Ka quantum number
52- 53 I2 --- Kc Kc quantum number
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Byte-by-byte Description of file (%): ph2o*.dat oh2o*.dat
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Bytes Format Units Label Explanations
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3- 5 I3 --- Trans Transition number
9- 10 I2 --- i Initial level
13- 14 I2 --- f Final level
18- 24 E7.2 cm3/s k20 Rate coefficient at 20K
26- 32 E7.2 cm3/s k100 Rate coefficient at 100K
34- 40 E7.2 cm3/s k200 Rate coefficient at 200K
42- 48 E7.2 cm3/s k400 Rate coefficient at 400K
50- 56 E7.2 cm3/s k800 Rate coefficient at 800K
58- 64 E7.2 cm3/s k1200 Rate coefficient at 1200K
66- 72 E7.2 cm3/s k1600 Rate coefficient at 1600K
74- 80 E7.2 cm3/s k2000 Rate coefficient at 2000K
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Acknowledgements:
Alexandre Faure, afaure(at)obs.ujf-grenoble.fr
History:
* 06-Sep-2007: Original level files
* 14-Mar-2008: More recent level files (oh2olev.dat and ph2olev.dat)
(End) Patricia Vannier [CDS] 15-Jun-2007