Issue |
A&A
Volume 397, Number 1, January I 2003
|
|
---|---|---|
Page(s) | 1 - 6 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361:20021508 | |
Published online | 11 December 2002 |
Decomposition dynamics of interstellar HCNH: Ab-initio MO and RRKM studies
1
Division of Molecular Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan
2
Nakanoshima Astronomical Observatory, Takao, Nakanoshima, Toshima, 891-5201, Japan
Corresponding author: Dr. H. Tachikawa, hiroto@eng.hokudai.ac.jp
Received:
23
April
2002
Accepted:
12
September
2002
Ab-initio MO calculations have been carried out for hydrogen-dissociation
reactions HCNH, i.e. (I) and
(II), in order
to elucidate the branching ratio of HCN/HNC on the ground state potential energy
surface. The calculations showed that the transition state for reaction I is lower in
energy than that of reaction II. The “bare” barrier heights for channel I and II were
calculated to be 33.5–34.8 kcal/mol and 38.5–40.7 kcal/mol, respectively. The energy
difference between transition states I and II was calculated to be 3.7–6.9 kcal/mol,
meaning that reaction I preferentially occurs in the threshold energy region.
Rice-Ramsperger-Kassel-Marcus (RRKM) theory including the tunneling effect
indicated that reaction I is more favorable than reaction II at lower energy region, if
tunneling effects are included in the rate calculations. On the other hand, the higher
energy region above ca. 50 kcal/mol, channel II became dominant. The branching ratio
(HCN/HNC) was calculated to be 0.3 at
eV, which corresponds to the electron
affinity of HCNH+. The mechanism of the reaction is discussed on the basis of
theoretical results.
Key words: molecular processes / ISM: molecules / molecular data
© ESO, 2003
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