A Quantum Rattleback Effect in Rotationally Asymmetric Molecules

The rattleback is a boat shaped toy with a non-uniform mass distribution. As a result, its principal axes of rotation do not coincide with geometrical symmetry axes. A rattleback exhibits unidirectional rotation when spun about a symmetry axis. Here we computationally investigate the rotational dynamics of C₂H₃Cl after interaction with a non-resonant, femtosecond laser pulse. C₂H₃Cl lacks an axis of rotational symmetry, as a result of which the principal axes of its moment of inertia and polarizability tensors do not coincide. The interaction with the laser pulse torques the molecule about the principal axes of the polarizability tensor, initiating rotation that is not about any one of the principal axes. We compute the time evolving probability distribution of molecular axes during and after this interaction by solving the Time Dependent Schrodinger Equation in the rigid rotor approximation. This probability distribution evidently exhibits a unidirectional rotational motion about the most polarizable molecular axis, similar to that of the classical rattleback. The effect can be traced back to Raman transitions occurring during interaction with the laser pulse that change the parity of K - the projection of the rotational angular momentum on the most polarizable axis.