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Vibronic Theory of Ultrafast Intersystem Crossing Dynamics in a Single Spin-Crossover Molecule at Finite Temperature beyond the Born–Oppenheimer Approximation
journal contribution
posted on 2016-02-02, 00:00 authored by Nikolay Klinduhov, Kamel BoukheddadenQuantum density matrix theory is
carried out to study the ultrafast
dynamics of the photoinduced state in a spin-crossover (SC) molecule
interacting with a heat bath. The investigations are realized at finite
temperature and beyond the usual Born–Oppenheimer (BO) approach.
We found that the SC molecule experiences in the photoexcited state
(PES) a huge internal pressure, estimated at several gigapascals,
partly released in an “explosive” way within ∼100
fs, causing large bond length oscillations, which dampen in the picosecond
time scale because of internal conversion processes. During this regime,
the BO approximation is not valid. Depending on the tunneling strength,
the ultrafast relaxation may proceed through the thermodynamic metastable
high-spin state or prevent it. Interestingly, we demonstrate that
final relaxation toward the low-spin state always follows a local
equilibrium pathway, where the BO approach is valid. Our formulation
reconciles the nonequilibrium and the equilibrium properties of this
fascinating phenomenon and opens the way to quantum studies on cluster
molecules.
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Keywords
tunneling strengthBO approachultrafast dynamicsphotoexcited stateconversion processesPESpicosecond time scalequantum studiescluster moleculesultrafast relaxationVibronic Theorybond length oscillationsequilibrium propertiesFinite TemperatureSC molecule experiencesUltrafast Intersystemequilibrium pathwayBO approximationheat bathphotoinduced state
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