Quantum dynamics study of fulvene double bond photoisomerization: The role of intramolecular vibrational energy redistribution and excitation energy
Résumé
The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop
optical control strategies based on the knowledge of the excited state decay mechanism. The decay
takes place on a time scale of several hundred femtoseconds, and the potential energy surface is
centered around a conical intersection seam between the ground and excited state. The competition
between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from
complete active space self-consistent field calculations, that captures the main features of the seam
(energy and locus of the seam and associated branching space vectors). Wave packet propagations
initiated by single laser pulses of 5–25 fs duration and 1.85–4 eV excitation energy show the principal
characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred
to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching
to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated
for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates,
which in turn depends on the excitation energy. These results set the ground for the development of
future optical control strategies.
Domaines
Chimie théorique et/ou physique
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