STSM by Tamas Rozgonyi, Research Centre for Natural Sciences of the Hungarian Academy of Sciences (HU) with Philipp Marquetand, University of Vienna (AT)
On April 24, 2017 (6 days)

Ab initio molecular dynamics simulations of photodissociation of halomethanes with SHARC

Dihalomethanes, such as CH2I2, have been popular benchmark systems of femtochemistry for a long time. Their photodissociation into different channels is essentially a multidimensional problem involving the stretching of both carbon-halogen bonds, bending of their bond angle and planarization of the main photofragment. The goal of the STSM was to initiate ab initio molecular dynamics simulations with the SHARC program package to get further insight into the dissociation dynamics governed by strong non-adiabatic effects and spin-orbit couplings.

The dynamics was first simulated by SHARC using the ab initio method, CASSCF, starting from the Franck-Condon region on bright singlet excited states. Potential energy scans with the more accurate and thus much more time-consuming ab initio method, CAPT2 along sample preliminary CASSCF trajectories have shown that using the higher level of theory is unevitable. A couple of trajectories have been obtained so far at the CASPT2 level, all showing vibrationally and rotationally hot CH2I formation.

While further trajectory computations are needed for reliable statistics on the possible outcomes of dissociation, Dyson norm computations for the relevant excited states at geometries along the trajectories are also in progress. This will enable a direct comparison between our simulations and the time-resolved photoelectron spectra recently obtained in pump-probe measurements by Prof. Thomas Weinacht at Stony Brook University.

Figure: The figure displays the energies of the adiabatic states along a SHARC / CASPT2 trajectory leading to ground state CH2I fragment and spin-orbit excited I atom. The energy of the active state governing the nuclear motion is displayed by black circles.


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