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Molecular Physics
An International Journal at the Interface Between Chemistry and Physics
Volume 121, 2023 - Issue 11-12: Special Issue of Molecular Physics in Honour of Péter Szalay
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Péter G. Szalay Special Issue of Molecular Physics

On the UV spectroscopy and photodynamics of octatetraene

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Article: e2132186 | Received 25 Aug 2022, Accepted 28 Sep 2022, Published online: 12 Oct 2022
 

Abstract

The UV absorption spectrum of all-trans-octatetraene is reinvestigated theoretically, focussing on the strongly dipole-allowed 1Ag1Bu transition. The dynamical calculations rely on ab initio multistate CASPT2 (MS-CASPT2) computations of the underlying potential energy surfaces and coupling elements, and the multiconfiguration time-dependent Hartree (MCTDH) method for solving the time-dependent Schrödinger equation for the nuclear motion. The vibronic structure of the absorption band near 2700 Å is well reproduced, better than ever before by a purely ab initio approach. The C–C single bond and C=C double bond stretching modes dominate the vibrational structure of the transition. While the latter resembles nearly harmonic motion on weakly coupled potential energy surfaces, the time-dependent calculations reveal a subpicosecond electronic population transfer from the 1Bu state to the lower-lying 2Ag state proceeding on a time scale of 50fs. The details of this internal conversion process and its relation to the conical intersection between the two excited states are discussed, paying particular attention to the impact of the 1Bu –2Ag energy gap on the dynamics.

GRAPHICAL ABSTRACT

Acknowledgments

This paper is dedicated to Prof. Peter G. Szalay on the occasion of his 60th birthday. We are indebted to Prof. Andreas Dreuw for valuable discussions and a careful reading of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Financial support by the Deutsche Forschungsgemeinschaft (Grant No. Ko945/23-1) is gratefully acknowledged.

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