Monday 31 October 2016
to 11:00 at
Morgane Vacher (Uppsala University and Imperial College London)
A photochemical process is a chemical reaction that is caused by the absorption of light and involves several electronic
states. In this presentation, we will focus on two types of photochemical processes. In the first part, we will discuss
coupled electron and nuclear dynamics following photoionisation. The hope to observe electronic motion on its own
time scale arose a few years ago in the field of attoscience. Several experiments have aimed to observe electron
dynamics following ionisation of molecules.1 Theoretical studies of pure electron dynamics in molecules have
predicted oscillatory charge migration,2 but often at just a single fixed nuclear geometry, i.e. neglecting both nuclear
motion and the natural nuclear distribution within the vibrational ground state wavepacket.3,4 Using our implementation
of the Ehrenfest method,5 we simulate pure electron dynamics in a substituted bismethylene-adamantane cation, and its
subsequent decoherence driven by nuclear motion and the natural zero point distribution in geometries.6 In the second
part of the presentation, we will discuss a “reversed photochemical process”, called chemiluminescence, where the
emission of light results from a chemical reaction. The basic understanding of today is that a thermally activated
molecule decomposes and by doing so, it undergoes a non-adiabatic transition to an electronic excited state of the
product (which then releases the excess energy in the form of light).7 To understand and rationalise experimental
observations, time and efforts were until now devoted to theoretically investigate the detailed nature of 1,2-dioxetane
molecule (the simplest light emitting species) and reaction mechanisms by computing cuts of potential energy surfaces
and identifying critical points and pathways.8,9 We aim to provide more insights of the chemiluminescence mechanism
by simulating the actual dynamics of the system.
1. F. Calegari et al, Science, 346, 336, 2014.
2. A. I. Kuleff and L. S. Cederbaum, J. Phys. B, 47, 124002, 2014.
3. M. Vacher, D. Mendive-Tapia, M. J. Bearpark and M. A. Robb, J. Chem. Phys., 142, 094105, 2015.
4. M. Vacher, L. Steinberg, A. J. Jenkins, M. J. Bearpark and M. A. Robb, Phys. Rev. A, 92, 040502(R), 2015.
5. M. Vacher, D. Mendive-Tapia, M. J. Bearpark and M. A. Robb, Theo. Chem. Acc., 113 1505, 2014.
6. M. Vacher, F. E. Albertani, A. J. Jenkins et al, Faraday Discuss., 10.1039/C6FD00067C, 2016.
7. I. Navizet, Y.-J. Liu, N. Ferré, D. Roca-Sanjuán and R. Lindh Chem. Phys. Chem., 12, P3064-3076, 2011.
8. L. De Vico, Y.-J. Liu, J. W. Krogh and R. Lindh, J. Phys. Chem. A, 111, 8013-8019, 2007.
9. P. Farahani, D. Roca-Sanjuán, F. Zapata and R. Lindh, J. Chem. Theory Comput., 9, 5404-5411, 2013