Simulation of the effect of vibrational pre-excitation on the dynamics of pyrrole photo-dissociation.

Dmitry V Makhov,Dmitrii V Shalashilin

doi:10.1063/5.0040178

Abstract

Photo-dissociation dynamics is simulated for vibrationally pre-excited pyrrole molecules using an ab initio multiple cloning approach. Total kinetic energy release (TKER) spectra and dissociation times are calculated. It is found that pre-excitation of N-H bond vibrations facilitates fast direct dissociation, which results in a significant increase in the high-energy wing of TKER spectra. The results are in very good agreement with the recent vibrationally mediated photo-dissociation experiment, where the TKER spectrum was measured for pyrrole molecules excited by a combination of IR and UV laser pulses. Calculations for other vibrational modes show that this effect is specific for N-H bond vibrations: Pre-excitation of other modes does not result in any significant changes in TKER spectra.

Highlights

Ultrafast excited state dynamics is key to understanding many important processes in chemistry and biochemistry, such as light harvesting in plants1 and visual reception.2 It plays an important role in the mechanisms of photoprotection,3 i.e., the processes that help biological molecules to minimize damage inflicted by UV light such as dissociation of the most important bonds.Total kinetic energy release (TKER) spectra and velocity map images (VMIs) are efficient experimental tools that can provide valuable information about ultrafast processes following photo-absorption
Calculated TKER spectra for the photo-dissociation of pyrrole with and without vibrational pre-excitation of mode 24 associated with N–H bond vibrations are presented in Fig. 2
These results are in extremely good agreement with experimental data for IR + UV photo-dissociation of pyrrole at λUV = 243 nm and νIR = 3532 cm−1 from Ref. 5 reproduced in Fig. 2: The difference is small for low energies, drops to near zero in the middle of the left slope of the line, and peaks with the maximum around the end of right slope

Summary

Introduction

Ultrafast excited state dynamics is key to understanding many important processes in chemistry and biochemistry, such as light harvesting in plants and visual reception. It plays an important role in the mechanisms of photoprotection, i.e., the processes that help biological molecules to minimize damage inflicted by UV light such as dissociation of the most important bonds.Total kinetic energy release (TKER) spectra and velocity map images (VMIs) are efficient experimental tools that can provide valuable information about ultrafast processes following photo-absorption. Ultrafast excited state dynamics is key to understanding many important processes in chemistry and biochemistry, such as light harvesting in plants and visual reception.. Ultrafast excited state dynamics is key to understanding many important processes in chemistry and biochemistry, such as light harvesting in plants and visual reception.2 It plays an important role in the mechanisms of photoprotection, i.e., the processes that help biological molecules to minimize damage inflicted by UV light such as dissociation of the most important bonds. Total kinetic energy release (TKER) spectra and velocity map images (VMIs) are efficient experimental tools that can provide valuable information about ultrafast processes following photo-absorption. The VMI/TKER methodology technique has been modified and developed further in the vibrationally mediated photo-dissociation (VMP) method, where, prior to UV photoexcitation, the molecule is excited vibrationally. It has been demonstrated that IR excitation of certain vibrational modes of pyrrole prior to UV excitation changes the shape of its TKER spectrum. As not all vibrational modes have the same effect on the photo-dissociation, the VMP technique can be used to study mode selective photochemistry

Methods

Results

Conclusion