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.

We demonstrate that strong laser pulses can induce torsional motion in a molecule consisting of a pair of phenyl rings. A nanosecond laser pulse spatially aligns the carbon-carbon bond axis, connecting the two phenyl rings, allowing a perpendicularly polarized, intense femtosecond pulse to initiate torsional motion accompanied by an overall rotation about the fixed axis. We monitor the induced motion by femtosecond time-resolved Coulomb explosion imaging. Our theoretical analysis accounts for and generalizes the experimental findings.

We present a study of multiphoton dissociative ionization from molecules. By solving the timedependent Schrödinger equation for H + 2 and projecting the solution onto double continuum scattering states, we observe the correlated electron-nuclear ionization dynamics in detail. We show -for the first time -how multiphoton structure prevails as long as the energies of all fragments are accounted for. Our current work provides a new avenue to analyze strong-field fragmentation that leads to a deeper understanding of the correlated molecular dynamics.PACS numbers: 31.15. 33.20.Wr, 33.20.Xx, 33.80.Rv Despite more than 20 years of scrutiny, strong-field dissociative ionization of molecules is still not completely understood. Understanding this process, however, would provide insight into how the energy deposited in the molecule by an intense laser pulse is shared between the electrons and the nuclei via their correlated motion. A large part of the challenge in investigating this process is that the dynamics of an ionized electron is not easily treated by the usual Born-Oppenheimer (BO) approximation. Complicating the issue further is the fact that the final state lies in at least a double continuum, likely Coulombic, comprised of the free nuclear and electronic motion which raises fundamental questions about the analysis.Because ab initio calculations of dissociative ionization require going beyond the BO approximation, the vast majority of intense field dissociative ionization calculations have been carried out for the simplest molecule: H + 2 (see, for example, Refs. [1][2][3]). Even for this system, however, full-dimensional solutions of the time-dependent Schrödinger equation (TDSE) have not yet been obtained in an intense field as they pose an immense computational challenge. Consequently, the dissociative ionization calculations that have been done simplified the problem even further through ad hoc reductions of the dimensionality or other severe approximations.Nevertheless, intense field processes identified via H [8,9] and applied to other systems [10,11]. More recently, two new models have been proposed to explain unexpected structure measured in the nuclear kinetic energy release (KER) spectrum following ionization of H + 2 . In one model, the interference of two dissociation pathways leads to the modulation of the KER spectrum via CREI [12,13]. The other model, named above threshold Coulomb explosion (ATCE), is based on the Floquet potentials obtained by dressing not only the field-free BO potentials but also the 1/R Coulomb explosion curve with photons from the laser field (see Fig. 4) [14]. The observed structure in the KER spectrum is thus due to absorption of different numbers of photons [14,15]. The predictions of the models deviate for low intensities and there is no consensus on which is correct. So, in addition to answering fundamental questions about electronnuclear correlations, TDSE solutions -along with an accurate way to analyze them -are needed to resolve this controversy.Key to understan...

It is demonstrated that strong laser pulses can introduce torsional motion in the axially chiral molecule 3,5-difluoro-3('),5(')-dibromobiphenyl. A nanosecond laser pulse spatially aligns the stereogenic carbon-carbon (C-C) bond axis allowing a perpendicularly polarized, intense femtosecond pulse to initiate torsional motion accompanied by a rotation about the fixed axis. We monitor the induced motion by femtosecond time-resolved Coulomb explosion imaging. Our theoretical analysis corroborates the experimental findings and on the basis of these results we discuss future applications of laser-induced torsion, viz., time-resolved studies of deracemization and laser controlled molecular junctions based on molecules with torsion.