Conical intersections and strong nonadiabatic coupling effects in singlet-excited acetylene: An ab initio quantum dynamical study

Horst Köppel, Bernd Schubert, Hans Lischka

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10 Scopus citations

Abstract

The conically intersecting potential energy surfaces of the S1 and S2 excited states of acetylene and the resulting strong nonadiabatic couplings are investigated theoretically. The adiabatic potential energy surfaces are obtained from high-level MRCI calculations. They are diabatized using the concept of regularized diabatic states and then used as a basis for the subsequent wave-packet dynamical treatment of the nuclear motion. All three angular degrees of freedom are included in the present study, while the bond lengths are kept frozen. The importance of the nonadiabatic interactions for the fine structure of the VUV spectrum of acetylene in the 6.5-8 eV excitation energy range is established. The electronic populations display an S2 → S1 internal conversion process on the order of 50 fs, which is, however, incomplete owing to the relatively small S2-S1 energy gap and the present reduced-dimensionality treatment. Snapshots of the wave-packet as well as angular probability densities are analyzed and reveal, for the first time, an incipient excited-state cis-trans isomerization in this system.

Original languageEnglish
Pages (from-to)319-328
Number of pages10
JournalChemical Physics
Volume343
Issue number2-3
DOIs
StatePublished - Jan 29 2008

Keywords

  • Acetylene
  • Conical intersections
  • Nonadiabatic dynamics
  • Wave-packet propagation

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