Isomerization HCN → HNC in the electronic ground state using chirp-optimized mid-IR pump and dump laser pulses: 3D quantum dynamics

Abstract

Starting from the full six nuclear-degrees-of-freedom (6D) Hamiltonian for HCN, reduced 4D and 3D Hamiltonians are systematically derived. Laser-induced isomerization for the planar fixed-CN orientation (3D) model is accomplished using a pump-dump scheme, where linear temporal chirps are optimized using several optimization methods. This includes a new implementation of the gradient-based GOAT algorithm in comparison to stochastic optimization. For the pump pulse, a (partial) vibrational-ladder climbing mechanism is demonstrated via the overtone bending modes, whereas the dump pulse populates several modes in addition to bending modes. The laser pulses should be straightforward to implement experimentally, and the efficacy of coherent (phase-only) laser control is demonstrated by comparison to an unchirped pulse with the same center frequency, pulse energy, and temporal shape.