Hansen, Jonas Lerche7; Nielsen, Jens Hedegaard8; Madsen, Christian Bruun3; Lindhardt, Anders Thyboe9; Johansson, Michael P.6; Skrydstrup, Troels10; Madsen, Lars Bojer8; Stapelfeldt, Henrik10
1 iNano-School, Science and Technology, Aarhus University2 Department of Physics and Astronomy, Science and Technology, Aarhus University3 Department of Physics and Astronomy, Faculty of Science, Aarhus University, Aarhus University4 Department of Chemistry, Science and Technology, Aarhus University5 Department of Engineering - Flow-proces Technology, Department of Engineering, Science and Technology, Aarhus University6 Institut de Química Computacional and Departament de Química, Universitat de Girona7 iNano-School, Science and Technology, Aarhus University8 Department of Physics and Astronomy, Science and Technology, Aarhus University9 Department of Engineering - Flow-proces Technology, Department of Engineering, Science and Technology, Aarhus University10 Department of Chemistry, Science and Technology, Aarhus University
We study how the combination of long and short laser pulses can be used to induce torsion in an axially chiral biphenyl derivative (3,5-difluoro-3′,5′-dibromo-4′-cyanobiphenyl). A long, with respect to the molecular rotational periods, elliptically polarized laser pulse produces 3D alignment of the molecules, and a linearly polarized short pulse initiates torsion about the stereogenic axis. The torsional motion is monitored in real-time by measuring the dihedral angle using femtosecond time-resolved Coulomb explosion imaging. Within the first 4 picoseconds (ps), torsion occurs with a period of 1.25 ps and an amplitude of 3° in excellent agreement with theoretical calculations. At larger times, the quantum states of the molecules describing the torsional motion dephase and an almost isotropic distribution of the dihedral angle is measured. We demonstrate an original application of covariance analysis of two-dimensional ion images to reveal strong correlations between specific ejected ionic fragments from Coulomb explosion. This technique strengthens our interpretation of the experimental data.
Journal of Chemical Physics, 2012, Vol 136, Issue 20