2016A&A...596A..35L


C.D.S. - SIMBAD4 rel 1.7 - 2019.10.14CEST08:54:00

2016A&A...596A..35L - Astronomy and Astrophysics, volume 596A, 35-35 (2016/12-1)

The ortho-to-para ratio of interstellar NH2: quasi-classical trajectory calculations and new simulations.

LE GAL R., HERBST E., XIE C., LI A. and GUO H.

Abstract (from CDS):

Based on recent Herschel results, the ortho-to-para ratio (OPR) of NH2 has been measured towards the following high-mass star-forming regions: W31C (G10.6-0.4), W49N (G43.2-0.1), W51 (G49.5-0.4), and G34.3+0.1. The OPR at thermal equilibrium ranges from the statistical limit of three at high temperatures to infinity as the temperature tends toward zero, unlike the case of H2. Depending on the position observed along the lines-of-sight, the OPR was found to lie either slightly below the high temperature limit of three (in the range 2.2-2.9) or above this limit (∼3.5, ≳4.2, and ≳5.0). In low temperature interstellar gas, where the H2 is para-enriched, our nearly pure gas-phase astrochemical models with nuclear-spin chemistry can account for anomalously low observed NH2-OPR values. We have tentatively explained OPR values larger than three by assuming that spin thermalization of NH2 can proceed at least partially by H-atom exchange collisions with atomic hydrogen, thus increasing the OPR with decreasing temperature. In this paper, we present quasi-classical trajectory calculations of the H-exchange reaction NH2+H, which show the reaction to proceed without a barrier, confirming that the H-exchange will be efficient in the temperature range of interest. With the inclusion of this process, our models suggest both that OPR values below three arise in regions with temperatures ≳20-25K, depending on time, and values above three but lower than the thermal limit arise at still lower temperatures.

Abstract Copyright: © ESO, 2016

Journal keyword(s): astrochemistry - ISM: molecules - submillimeter: ISM - molecular processes - line: formation

Simbad objects: 7

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Number of rows : 7

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2019
#notes
1 Barnard 1 MoC 03 33 16.3 +31 07 51           ~ 243 0
2 NAME Horsehead Nebula DNe 05 40 59.0 -02 27 30           ~ 430 0
3 IRAS 16293-2422 cor 16 32 22.56 -24 28 31.8           ~ 997 1
4 W 31c HII 18 10 29.1 -19 56 05           ~ 298 0
5 OH 34.26 +0.15 SFR 18 53 18.54 +01 14 57.9           ~ 448 0
6 W 49n HII 19 10 13.2 +09 06 12           ~ 403 3
7 W 51 SNR 19 23 50 +14 06.0           ~ 1118 1

    Equat.    Gal    SGal    Ecl

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2019.10.14-08:54:00

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