Detecting Chirality in Molecules by Linearly Polarized Laser Fields

Abstract

A new scheme for enantiomer differentiation of chiral molecules using a pair of linearly polarized intense ultrashort laser pulses with skewed mutual polarization is presented. The technique relies on the fact that the off-diagonal anisotropic contributions to the electric polarizability tensor for two enantiomers have different signs. Exploiting this property, we are able to excite a coherent unidirectional rotation of two enantiomers with a π phase difference in the molecular electric dipole moment. The approach is robust and suitable for relatively high temperatures of molecular samples, making it applicable for selective chiral analysis of mixtures, and to chiral molecules with low barriers between enantiomers. As an illustration, we present nanosecond laser-driven dynamics of a tetratomic nonrigid chiral molecule with short-lived chirality. The ultrafast time scale of the proposed technique is well suited to study parity violation in molecular systems in short-lived chiral states.

Laser-induced persistent orientation of chiral molecules

“…Recently, a pair of non-resonant delayed crosspolarized laser pulses was proposed as a new tool for discrimination of chiral molecules [23][24][25] and the underlying classical enantioselective molecular orientation mechanism was exposed [24,25]. The approach was extended to general fields with time-dependent polarization twisting in a plane.…”

Controlled Enantioselective Orientation of Chiral Molecules with an Optical Centrifuge

“…A unified analysis of this new class of chiral measurements without magnetic interactions can be found in Ref. 35. Recently, a new set of methods has been theoretically proposed for detecting molecular chirality by enantioselective orientation of chiral molecules with strong nonresonant laser fields [36][37][38]. When linearly polarized, such fields can align an ensemble of molecules along their polarization direction, whereas orienting the molecules is impossible due to the symmetry of the field interaction with the induced dipole.…”

“…The average alignment factor for C + rises above the isotropic value much faster, explaining why its dipping below 0.5 was not observed experimentally. Moreover, the predicted rotation-induced enantioselective molecular orientation [36][37][38] is indeed imprinted in the orientation of the fragment velocities, thus appearing in both the calculated and measured velocity distributions. Most importantly and similar to the experiment, the sign of the calculated ∆ sin(θ 2D ) for the C + fragment is opposite to that of O + , confirming the orientation of the molecular b axis along or against the propagation direction of the centrifuge.…”

Simulating electric field interactions with polar molecules using spectroscopic databases

“…In all calculations we fixed to 4 ps. For simulations of the mixed Raman-THz field-free orientation of PH 3 , the lack of a polarizability model in the ExoMol database meant the simulations of the initial Raman excitation were carried out using a more general variational approach implemented in the TROVE6 and RichMol program packages. The resulting wavepacket was then used as the initial wavefunction in subsequent THz-driven dynamics simulations, modelled using the ExoMol line list data.…”