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J/MNRAS/399/425    (De)excitation rates of ortho-NH3 and para-NH3 (Faure+, 2009)

On the robustness of the ammonia thermometer. Maret S., Faure A., Scifoni E., Wiesenfeld L. <Mon. Not. R. Astron. Soc. 399, 425 (2009)> =2009MNRAS.399..425M
ADC_Keywords: Atomic physics Keywords: molecular data - molecular processes - ISM: molecules Abstract: Ammonia inversion lines are often used as probes of the physical conditions in the dense ISM. The excitation temperature between the first two para metastable (rotational) levels is an excellent probe of the gas kinetic temperature. However, the calibration of this ammonia thermometer depends on the accuracy of the collisional rates with H2. Here we present new collisional rates for ortho-NH3 and para-NH3 colliding with para-H2 (J=0) and we investigate the effects of these new rates on the excitation of ammonia. Scattering calculations employ a new, high accuracy, potential energy surface computed at the coupled-cluster CCSD(T) level with a basis set extrapolation procedure. Rates are obtained for all transitions involving ammonia levels with J≤3 and for kinetic temperatures in the range 5-100K. We find that the calibration curve of the ammonia thermometer -- which relates the observed excitation temperature between the first two para metastable levels to the gas kinetic temperature -- does not change significantly when these new rates are used. Thus, the calibration of ammonia thermometer appears to be robust. Effects of the new rates on the excitation temperature of inversion and rotation-inversion transitions are also found to be small. Description: For ortho- and para-NH3, 15 and 45 *downward* rotational rates are provided, corresponding to all possible transitions among their 6 and 10 lowest levels, respectively. 20 temperatures in the range 5-100K are considered. Upward rates can be computed using the detailed balance relation (see paper). Level energies are from the JPL catalog. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file onh3lev.dat 37 6 Energy levels of ortho-NH3, in cm-1 pnh3lev.dat 37 10 Energy levels of para-NH3, in cm-1 onh3ph2.dat 208 15 De-excitation rates (in cm3/s) of ortho-NH3 in collision with para-H2 pnh3ph2.dat 208 45 De-excitation rates (in cm3/s) of para-NH3 in collision with para-H2
See also: J/A+A/472/1029 : (De)excitation rates of H2O by H2 (Faure+, 2007) 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) Byte-by-byte Description of file (# headlines): onh3lev.dat pnh3lev.dat
Bytes Format Units Label Explanations
1- 5 I5 --- Level [1,10] level number 6- 21 F16.9 cm-1 E level energy 22- 28 F7.1 --- F statistical weight 29- 37 A9 --- N quantum numbers
Byte-by-byte Description of file (# headlines): onh3ph2.dat pnh3ph2.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Trans [1,45] Transition number 4- 5 I2 --- i [2,10] Initial level 7- 8 I2 --- f [1,10] Final level 10- 18 E9.3 cm3/s k5 Rate coefficient at 5K 20- 28 E9.3 cm3/s k10 Rate coefficient at 10K 30- 38 E9.3 cm3/s k15 Rate coefficient at 15K 40- 48 E9.3 cm3/s k20 Rate coefficient at 20K 50- 58 E9.3 cm3/s k25 Rate coefficient at 25K 60- 68 E9.3 cm3/s k30 Rate coefficient at 30K 70- 78 E9.3 cm3/s k35 Rate coefficient at 35K 80- 88 E9.3 cm3/s k40 Rate coefficient at 40K 90- 98 E9.3 cm3/s k45 Rate coefficient at 45K 100-108 E9.3 cm3/s k50 Rate coefficient at 50K 110-118 E9.3 cm3/s k55 Rate coefficient at 55K 120-128 E9.3 cm3/s k60 Rate coefficient at 60K 130-138 E9.3 cm3/s k65 Rate coefficient at 65K 140-148 E9.3 cm3/s k70 Rate coefficient at 70K 150-158 E9.3 cm3/s k75 Rate coefficient at 75K 160-168 E9.3 cm3/s k80 Rate coefficient at 80K 170-178 E9.3 cm3/s k85 Rate coefficient at 85K 180-188 E9.3 cm3/s k90 Rate coefficient at 90K 190-198 E9.3 cm3/s k95 Rate coefficient at 95K 200-208 E9.3 cm3/s k100 Rate coefficient at 100K
Acknowledgements: Alexandre Faure, afaure(at)
(End) Alexandre Faure [LAOG, France], Patricia Vannier [CDS] 24-Sep-2009
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