The availability of short, intense laser pulses has opened up new frontiers in chemistry and physics. Attosecond laser pulses can directly explore electron dynamics, image molecular orbitals and probe bond making and breaking processes. Intense femtosecond laser pulses can act as photonic reagents by selectively altering the nuclear and electronic dynamics of molecules. The response of molecules to short, intense laser pulses cannot be treated by the perturbative methods used for ordinary spectroscopy. Direct simulation of the dynamics is needed to understand the behaviour of molecules under these extreme conditions. Short, intense laser pulses in the optical range cause rapid ionization. We have used time-dependent configuration interaction with absorbing boundaries to simulate the ionization and find that strong field ionization rates depend markedly on the conjugation length of the molecule and the orientation of the molecule in the laser beam. The shapes of the ionization yield for linearly polarized light can be understood primarily in terms of the nodal structure of the highest occupied orbitals. Depending on the orbital energies, ionization from lower lying orbitals may also make significant contributions to the shapes. The shapes of the ionization yield for circularly polarized light can be readily explained in terms of the shapes for linearly polarized light. In the mid IR range, short intense laser pulses can rapidly deposit substantial amounts of vibrational energy into specific parts of a molecule. Such highly energized molecules can undergo fast rearrangements and selective dissociations. We have used ab initio classical trajectory calculations in time-varying electric fields to examine the fragmentation of molecules in intense IR laser pulses.

Computational simulation of molecules interacting with intense laser fields

256th National Meeting (2018)

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