Control and femtosecond time-resolved imaging of torsion in a chiral molecule

Abstract

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.

Incorporating real time velocity map image reconstruction into closed-loop coherent control

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Alignment enhancement of molecules embedded in helium nanodroplets by multiple laser pulses

“…The ability to align molecules, i.e., confine their axes with respect to axes defined in the laboratory frame, can be of great use in studies of the structure [1,2] and dynamics [3,4] of molecules. Among several methods, alignment induced by nonresonant, moderately intense laser pulses [5] has proven very versatile and efficient for isolated molecules and, as a result, found widespread applications in a variety of areas in molecular science.…”

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

“…Covariance mapping has been extended from diatomics to triatomic molecules [172,173] and has also been applied to photoelectron spectroscopy [174]. Recently the technique has also been demonstrated for angularly resolved photo-ion spectra obtained with a velocity map imaging spectrometer [175].…”