Demos.MolRotation.Main

WavePacket demo examples: Molecular rotation

Also external degrees of freedom of molecules can be manipulated by electromagnetic fields. In particular, interaction with intense light fields can be used to rotate molecules with respect to the polarisation axis of the light. Using modern laser technology, it is possible to align molecules or to create rotational wavepackets thus giving rise to well-known revival phenomena. Since the Hamiltonian in spherical coordinates can be difficult to treat with Fourier-based grid methods, we use an DVR/FBR expansion in spherical harmonics that is also built-in in WavePacket.

Test for DVR/FBR representation

WavePacket comes with a special DVR/FBR representation for expanding states in associated Legendre functions in cos θ (proportional to spherical harmonics Y_lm with constant m, i.e., cylindrical symmetry around the z axis). Here, we want to use this representation to compare with results from the literature, where the energies of stationary states are extracted from Fourier transforms of the autocorrelation obtained from solutions of the time-dependent Schrödinger equation, as well as direct solutions of the time-independent Schrödinger equation. Learn more ...

Rotational dynamics of linear molecules

When a molecule is irradiated by intense laser light, it will undergo a Raman-type transition. In other words, the laser will induce a dynamic dipole moment in the molecule, which in turn interacts with the electric field. This second order effect then leads to alignment of the molecule. If a (linearly polarized) laser is turned on slowly, molecules align along the laser polarization axis with each rotational eigenstate adiabatically evolving into a pendular state. However, in the case of a nonadiabatic (fast) laser turn-on, the interaction creates rotational wavepackets that show significant alignment even after the laser has been turned off. Eventually, this leads to revival phenomena, i.e. spontaneous re-alignment under field-free conditions. Learn more ...