Rotational excitation of molecular ions in interstellar clouds

1975 ◽  
Vol 201 ◽  
pp. 366 ◽  
Author(s):  
S. Green
Keyword(s):  
Molecular Ions ◽  
Rotational Excitation ◽  
Interstellar Clouds

Rotational excitation of molecular ions by electron impact under interstellar conditions

1981 ◽  
Vol 247 ◽  
pp. 936 ◽  
Author(s):  
S. S. Bhattacharyya ◽  
B. Bhattacharyya ◽  
M. V. Narayan
Keyword(s):  
Electron Impact ◽  
Molecular Ions ◽  
Rotational Excitation

scholarly journals Deuterated forms of H 3 + and their importance in astrochemistry

2019 ◽  
Vol 377 (2154) ◽  
pp. 20180401 ◽  
Author(s):  
P. Caselli ◽  
O. Sipilä ◽  
J. Harju
Keyword(s):  
Chemical Species ◽  
Branching Ratio ◽  
Spin Symmetry ◽  
Atomic Ratio ◽  
Molecular Ions ◽  
Diagnostic Tools ◽  
Interstellar Clouds ◽  
Cosmic Abundance ◽  
Cloud Cores ◽  
Dust Grain

At the low temperatures (approx. 10 K) and high densities (approx. 100 000 H 2 molecules per cm −3 ) of molecular cloud cores and protostellar envelopes, a large amount of molecular species (in particular those containing C and O) freeze-out onto dust grain surfaces. It is in these regions that the deuteration of H 3 + becomes very efficient, with a sharp abundance increase of H 2 D + and D 2 H + . The multi-deuterated forms of H 3 + participate in an active chemistry: (i) their collision with neutral species produces deuterated molecules such as the commonly observed N 2 D + , DCO + and multi-deuterated NH 3 ; (ii) their dissociative electronic recombination increases the D/H atomic ratio by several orders of magnitude above the D cosmic abundance, thus allowing deuteration of molecules (e.g. CH 3 OH and H 2 O) on the surface of dust grains. Deuterated molecules are the main diagnostic tools of dense and cold interstellar clouds, where the first steps toward star and protoplanetary disc formation take place. Recent observations of deuterated molecules are reviewed and discussed in view of astrochemical models inclusive of spin-state chemistry. We present a new comparison between models based on complete scrambling (to calculate branching ratio tables for reactions between chemical species that include protons and/or deuterons) and models based on non-scrambling (proton hop) methods, showing that the latter best agree with observations of NH 3 deuterated isotopologues and their different nuclear spin symmetry states. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.

Electron-impact rotational excitation of : relevance for thermalization and dissociation dynamics

2006 ◽  
Vol 364 (1848) ◽  
pp. 3113-3120 ◽  
Author(s):  
Alexandre Faure ◽  
Laurent Wiesenfeld ◽  
Pierre Valiron ◽  
Jonathan Tennyson
Keyword(s):  
Dissociative Recombination ◽  
Molecular Ions ◽  
Rate Coefficients ◽  
Galactic Centre ◽  
Low Density ◽  
Rotational Excitation ◽  
Astrophysical Plasmas ◽  
Electron Collisions ◽  
Dissociation Dynamics ◽  
Rotational Distribution

Electrons are known to be efficient in rotationally exciting molecular ions in low-density astrophysical plasmas. Rotational excitation of molecular ions has also been shown to affect the measured values of dissociative recombination (DR) rate coefficients. Thus, electron collisions with are expected to play a significant role in thermalization and dissociation dynamics of this ion, both in the laboratory and in space. Using the molecular R -matrix method combined with the adiabatic-nuclei-rotation approximation, we have computed new rate coefficients for the rotational excitation of by electrons at temperatures from 10 to 10 000 K. De-excitation rates are found to amount to a few 10 −7  cm 3  s −1 below 1000 K, i.e. comparable in magnitude to that of DR. In astrophysical environments where the electron fraction exceeds 10 −4 , electron collisions are thus expected to contribute to the non-thermal rotational distribution of . The competition between electron and neutral collisions is discussed in the context of recent observations of towards Galactic centre sources.

scholarly journals Rotational excitation of interstellar molecular ions by electrons

2009 ◽  
Vol 192 ◽  
pp. 012016 ◽  
Author(s):  
A Faure ◽  
J Tennyson ◽  
V Kokoouline ◽  
Chris H Greene
Keyword(s):  
Molecular Ions ◽  
Rotational Excitation
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