Electronic and non-adiabatic dynamics: general discussion

Abstract

Miller remarked: How did you damp the mode? Was the parameter based on physically reasonable damping, presumably to the bath (system-bath coupling). The reason I ask is that normally vibrational damping times for relatively high frequency coupling modes are on the order of ps relative to much faster motions to the CI region. This mechanism may not be operative. Maxim Gelin responded:We considered a minimal model of a so-called dissipative conical intersection. Namely, two coupled electronic states and two vibrational modes are considered as the system, which is bilinearly coupled to an environment. The results of our studies demonstrate that the conical intersection induces highly non-linear dynamics which is very sensitive to even weak coupling † Wolfgang Domcke's paper was presented by Maxim Gelin, Technische Universit¨at Munchen,¨ Garching, Germany.to the bath. If the electronic coupling at the conical intersection were set to zero, the weakest system-bath couplings considered in the present work would virtu-ally produce no eff ect on the wavepacket dynamics on a picosecond timescale. The dynamics at the conical intersection, on the contrary, is highly non-linear and chaotic and hence very sensitive to even weak system-bath couplings.Andrew Orr-Ewing asked: Can your results for a conical intersection which is bound along both the tuning and coupling coordinates provide some insights about the role of a dissipative medium on the dynamics of passage through a conical intersection in which the tuning coordinate is dissociative? For example, can we learn something about how a solvent aff ects the non-adiabatic dissocia-tion of heteroaromatic molecules excited to repulsive ps* states?Maxim Gelin answered: The role of vibrational energy relaxation due to the coupling to a vibrational bath in photodissociation reactions driven by repulsive ps* states was explored for a model of the photodissociation of pyrrole by Lan and Domcke. 1 It was shown that sufficiently strong system-bath coupling reduces the dissociation probability and enhances the probability for internal conversion to the electronic ground state. This nding is in qualitative agreement with the experimental observation that H-atom photodetachment via dissociative ps* states is suppressed in larger chromophores with more vibrational degrees of freedom, see e.g., M.-F. Lin et al.2 While H-atom photodetachment is the domi-nant photochemical channel in pyrrole and indole, it is completely quenched in tryptophan and larger chromophores. Dmitrii Shalashilin commented: Is the computational approach you are using generic or can it only be used for speci c types of Hamiltonian?Maxim Gelin replied: The approach assumes that the bath is described by a collection of harmonic oscillators and the system bath coupling is linear in the bath coordinates. The system Hamiltonian may be quite general.Adam Kirrander remarked: Could one adapt your model of a bath to describe a speci c system, for instance, a particular solvent or an anisotropic environment such as a protein em...

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