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 proceed ing in the electronic ground state is simulated for HCN-->HNC isomeriz ation. The simulation is based on global 3D ab initio electronic groun d state potential and dipole surfaces. The dipole surface obtained as part of the present work is a fit to 2010 single-reference AQCC data p oints. 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 las er polarization is fixed along the CN axis and molecular rotation is d isregarded. Isomerization is initiated from HCN in its (J=0) vibration al ground state, and control is exerted by a pulse sequence which spli ts the overall process into a sequence of state-specific sub-transitio ns. The intermediate states are chosen from a least-cost isomerization ladder obtained from an artificial intelligence algorithm, and includ e excited HCN bend states and a delocalized vibrational state above th e isomerization barrier. We demonstrate that the molecule can be prepa red in a specified HNC bend state with high overall selectivity (>92%) and without concomitant ionization or dissociation, on a picosecond t imescale using 4 or 5 sequential mid-infrared Gaussian pulses.