A simulation of ultrafast state-selective IR-laser-controlled isomerization of hydrogen cyanide based on global 3D ab initio potential and dipole surfaces

An ultrafast state-selective laser-controlled pump-dump scheme proceeding in the electronic ground state is simulated for HCN-->HNC isomerization. The simulation is based on global 3D ab initio electronic ground state potential and dipole surfaces. The dipole surface obtained as part of the present work is a fit to 2010 single-reference AQCC data points. Isomerization dynamics including all three vibrational degrees of freedom is treated within the J=0 vibrational marlifold. Up to 550 J=0 vibrational states previously reported by Bowman et al. [J. Chem. Phys. 99 (1993) 308] are employed to obtain converged results. The laser polarization is fixed along the CN axis and molecular rotation is disregarded. Isomerization is initiated from HCN in its (J=0) vibrational ground state, and control is exerted by a pulse sequence which splits the overall process into a sequence of state-specific sub-transitions. The intermediate states are chosen from a least-cost isomerization ladder obtained from an artificial intelligence algorithm, and include excited HCN bend states and a delocalized vibrational state above the isomerization barrier. We demonstrate that the molecule can be prepared in a specified HNC bend state with high overall selectivity (>92%) and without concomitant ionization or dissociation, on a picosecond timescale using 4 or 5 sequential mid-infrared Gaussian pulses.