Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003a%26a...397....1t&link_type=abstract
Astronomy and Astrophysics, v.397, p.1-6 (2003)
Astronomy and Astrophysics
Astrophysics
3
Molecular Processes, Ism: Molecules, Molecular Data
Scientific paper
Ab-initio MO calculations have been carried out for hydrogen-dissociation reactions HCNH, i.e. HCNH -> H + HCN (I) and HCNH -> HNC + H (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 E = 4.4 eV, which corresponds to the electron affinity of HCNH+. The mechanism of the reaction is discussed on the basis of theoretical results.
Fukuzumi T.
Iyama T.
Tachikawa H.
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