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Astrophysics and Space Science

, Volume 236, Issue 1, pp 29–47 | Cite as

Non-adiabatic interactions in excitedC2H molecules and their relationship toC2 formation in comets

  • William M. Jackson
  • Victor Blunt
  • Hua Lin
  • Martina Green
  • Gregory Olivera
  • William H. Fink
  • Yihan Bao
  • Randall S. Urdahl
  • Fida Mohammad
  • Mansour Zahedi
Article

Abstract

A unified picture of the photodissociation of theC2H radical has been developed using the results from the latest experimental and theoretical work. This picture shows that a variety of electronic states ofC2 are formed during the photodissociation of theC2H radical even if photoexcitation accesses only one excited state. This is because the excited states have many avoided corssings and near intersections where two electronic states come very close to one another. At these avoided crossings and near intersections, the excited radical can hop from one electronic state to another and access new final electronic states of theC2 radical. The complexity of the excited state surfaces also explains the bimodal rotational distributions that are observed in all of the electronic states studied. The excited states that dissociate through a direct path are limited by dynamics to produceC2 fragments with a modest amount of rotational energy, whereas those that dissociate by a more complex path have a greater chance to access all of phase space and produce fragments with higher rotational excitation. Finally, the theoretical transition moments and potential energy curves have been used to provide a better estimate of the photochemical lifetimes in comets of the different excited states of theC2H radical. The photochemically active states are the 22+, 22II, 32II, and 32+, with photodissociation rate constants of 1.0×10−6, 4.0×10−6, 0.7×10−6, and 1.3×10−6s−1, respectively. These rate constants lead to a total photochemical lifetime of 1.4×105 s.

Keywords

Excited State Electronic State Photodissociation Potential Energy Curve Rotational Energy 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 1996

Authors and Affiliations

  • William M. Jackson
    • 1
  • Victor Blunt
    • 1
  • Hua Lin
    • 1
  • Martina Green
    • 1
  • Gregory Olivera
    • 1
  • William H. Fink
    • 1
  • Yihan Bao
    • 1
  • Randall S. Urdahl
    • 1
  • Fida Mohammad
    • 1
  • Mansour Zahedi
    • 1
  1. 1.Department of ChemistryUniversity of CaliforniaDavis

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