Torsional and rotational coupling in non-rigid molecules

TL;DR

This paper investigates how torsional and rotational motions in non-rigid molecules are coupled, especially when electronic state transitions alter torsional potentials, affecting molecular structure and rotational dynamics.

Contribution

It provides a theoretical analysis of torsional-rotational coupling in non-rigid molecules during electronic state transitions induced by laser pulses.

Findings

Torsional wavepacket motion influences the molecule's inertia tensor.

Electronic state changes significantly affect rotational wave functions.

The study highlights the impact of torsional potentials on rotational dynamics.

Abstract

We analyze theoretically the interplay between the torsional and the rotational motion of an aligned biphenyl-like molecule. To do so, we consider a transition between two electronic states with different internal torsional potentials, induced by means of a resonant laser pulse. The change in the internal torsional potential provokes the motion of the torsional wavepacket in the excited electronic state, modifying the structure of the molecule, and hence, its inertia tensor. We find that this process has a strong impact on the rotational wave function, displaying different behavior depending on the electronic states involved and their associated torsional potentials. We describe the dynamics of the system by considering the degree of alignment and the expectations values of the angular momentum operators for the overall rotation of the molecule.