Walt Samuel G, Bhargava Ram N, von Conta Aaron, Tolstikhin Oleg I, Madsen Lars Bojer, Jensen Frank, Wörner Hans Jakob
Laboratorium für Physikalische Chemie, ETH Zürich , 8093 Zürich, Switzerland.
Moscow Institute of Physics and Technology , Dolgoprudny 141700, Russia.
J Phys Chem A. 2015 Dec 10;119(49):11772-82. doi: 10.1021/acs.jpca.5b07331. Epub 2015 Nov 24.
We report angle- and momentum-resolved measurements of the dissociative ionization and Coulomb explosion of methyl halides (CH3F, CH3Cl, CH3Br, and CH3I) in intense phase-controlled two-color laser fields. At moderate laser intensities, we find that the emission asymmetry of low-energy CH3(+) fragments from the CH3(+) + X(+) (X = F, Cl, Br, or I) channel reflects the asymmetry of the highest occupied molecular orbital of the neutral molecule with important contributions from the Stark effect. This asymmetry is correctly predicted by the weak-field asymptotic theory, provided that the Stark effect on the ionization potentials is calculated using a nonperturbative multielectron approach. In the case of high laser intensities, we observe a reversal of the emission asymmetries for high-energy CH3(+) fragments, originating from the dissociation of CH3X(q+) with q ≥ 2. We propose ionization to electronically excited states to be at the origin of the reversed asymmetries. We also report the measurements of the emission asymmetry of H3(+), which is found to be identical to that of the low-energy CH3(+) fragments measured at moderate laser intensities. All observed fragmentation channels are assigned with the help of CCSD(T) calculations. Our results provide a benchmark for theories of strong-field processes and demonstrate the importance of multielectron effects in new aspects of the molecular response to intense laser fields.
