Theory of torsional control for G₁₆-type molecules

We introduce a four-dimensional quantum model for describing the torsional control with moderately strong, non-resonant laser pulses of G₁₆-type molecules in the electronic ground state, based on the symmetry-adapted variational method. We define conditions for which lower-dimensional models, commonly used to simulate the strong-field control of molecular torsions, are reliable approximations to a four-dimensional treatment. In particular, we study the role of different types of rotational-torsional couplings - the field-free coupling and the field-induced coupling - and show that the conclusions recently drawn on the role of rotational-torsional couplings in the process of torsional alignment are not correct in general. Furthermore, we demonstrate how important an adequate description of the molecular polarizability is for reliably predicting the torsional alignment.