STSM by Judith Dura, MBI – Nonlinear optics and Short Pulse Spectroscopy (DE) with Luis Bañares, Universidad Complutense de Madrid (ES)
On April 13, 2016 (10 days)

New energy transfer mechanisms in methyl iodide complexes unravel by femtosecond Coulomb repulsion

Multiphoton processes in atoms and molecules are highly probable upon ultrashort laser pulses irradiation. When the molecule is a Van der Waals cluster, there is a certain probability that within the same aggregate, one monomer experiences a neutral fragmentation channel, and a different monomer suffers an ionizing process. Within this particular situation, if a second laser pulse arrives it will ionize the fragment under neutral dissociation, which will experience a Coulomb repulsive force with the charge neighbour. Thus, the kinetic energy of the dissociated fragment will be modified as a function of the distance between the charge fragments. The kinetic energy trace of the Coulomb repulsed particles can be followed in time, i.e. charge particles distance, using the combination of ultrashort laser pump-probe techniques together with Velocity Map Imaging detection systems.
Figures 1 show 2D contour maps of the Centre of Mass (CM) kinetic energy (KE) of CH3 as a function of the time delay for λpump = 266 nm and λprobe = 333.5 nm a. Three time-dependent KE contributions can be distinguished.

Figure 1. Time-dependent ionization yield and Centre of Mass (CM) kinetic energy (KE) of photodissociation CH3 fragments at λpump = 266 nm and λprobe = 333.5 nm. Letters indicate time-dependent Coulomb repulsion trajectories.




Coulomb repulsion trajectories for the CH3 fragment in repulsion with the other CH3I of the dimer were simulated for the most stable dimer geometries (details of the calculations not given here) and compared with the experimental Coulomb repulsion trajectories.
The comparison suggest that trajectories A and B converge asymptotically to the neutral dissociation channels of the CH3I in the A-band.
An article with the outcome of this STSM has been writing at the moment to be send to Phys. Chem. Chem. Phys. in the next incoming months.

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