Viscosity dependence of internal conversion rates of polyatomic molecules

AbstractA general framework for the simulation of ultrafast pump-probe time resolved experiments based on Born-Oppenheimer molecular dynamics (BOMD) is presented. Interaction of the molecular species with a laser is treated by a simple maximum entropy distribution of the excited state occupancies. The latter decay of the electronic excitation into the vibrations is based on an on-the-fly estimation of the rate of the internal conversion, while the energy is distributed in a thermostat-like fashion. The approach was tested by reproducing the results of previous femtosecond studies on ethylene, naphthalene and new results for phenanthrene.

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Evaluating the Anharmonicity Contributions to the Molecular Excited State Internal Conversion Rates with Finite Temperature TD-DMRG

10.26434/chemrxiv.14356628.v1 ◽

2021 ◽

Author(s):

Yuanheng Wang ◽

Jiajun Ren ◽

Zhigang Shuai

Keyword(s):

Excited State ◽

Excitation Energy ◽

Internal Conversion ◽

Energy Levels ◽

Harmonic Approximation ◽

Transition Process ◽

High Energy ◽

Electronic Energy ◽

Relaxation Rates ◽

Conversion Rates

<div>In this work, we propose a new method to calculate the molecular nonradiative electronic relaxation rates based on the numerically exact time-dependent density matrix renormalization group theory (TD-DMRG). This method could go beyond the existing frameworks under the harmonic approximation (HA) of the potential energy surface (PES) so that the important anharmonic effect could be considered when large electronic energy is transferred into the vibrations to excite them to the high energy levels. The effectiveness and scalability of the method are verified in calculating the internal conversion (IC) rate of azulene by comparing it with the analytically exact results under HA. Furthermore, we investigate the validity of HA in a two-mode model with Morse potential. We find that HA is unsatisfactory unless only the lowest several vibrational states of the lower electronic state are involved in the transition process when the adiabatic excitation energy is relatively low. As the excitation energy increases, HA first underestimates and then overestimates the IC rates when the excited state PES shifts towards the dissociative side of the ground state PES. On the contrary, HA slightly overestimates the IC rates when the excited state PES shifts towards the repulsive side. In both cases, higher temperature enlarges the error of HA. <br></div>

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Quantum Control of Ultrafast Internal Conversion using Nano-Confined Virtual Photons

10.26434/chemrxiv.11164796 ◽

2019 ◽

Author(s):

Aleksandr Avramenko ◽

Aaron Rury

Keyword(s):

Quantum Control ◽

Internal Conversion ◽

Structural Changes ◽

Radiative Relaxation ◽

Rabi Splitting ◽

Conversion Rates ◽

Tetraphenyl Porphyrin ◽

Virtual Photons ◽

Theoretical Predictions ◽

Vacuum Rabi Splitting

<div> <div> <div> <p>The rational control of non-radiative relaxation remains an unfulfilled goal for synthetic chemistry. In this study, we show strongly coupling an ensemble of molecules to the virtual photons of an electromagnetic cavity provides a rational handle over ultrafast, non-radiative dynamics. Specifically, we control the concentration of zinc tetraphenyl porphyrin molecules within nano-scale Fabry-Perot cavity structures to show a variable collective vacuum Rabi splitting between the polaritons coincides with changes in internal conversion rates. We find these changes obey a power law dependence on the collective vacuum Rabi splitting, but de- viate from the predictions of so-called gap laws. We also show simple theories of structural changes caused by polariton formation cannot explain discrepancies between our results and established theoretical predictions. Our results demonstrate a mechanism by which cavity polariton formation controls the fundamental photo-physics of light harvesting and photo- catalytic molecular moieties and the gap remaining in our fundamental understanding of these mechanisms. </p> </div> </div> </div>

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