Quantum control study of ultrafast isotope-selective vibrational excitations of the cesium iodide (CsI) molecule

We study, using quantum optimal control theory (OCT), isotope-selective vibrational excitations on the ground-state potential energy curve for the mixture of two pure ensembles for cesium iodide isotopomers (133CsI and 135CsI). In the present OCT calculations initial states are set to the condition that both 133CsI and 135CsI are in the vibrational ground level, i.e., (v133, v135) = (0, 0), and target states are set to three: (v133, v135) = (0, 2), (0, 3), and (0, 4), where molecular orientations are fixed parallel to the field polarization vector. Three total times (i.e., pulse durations), T = 460 000 au (∼11.1 ps), 920 000 au (∼22.2 ps), and 1 840 000 au (∼44.5 ps), are set in the calculations and nine cases for the combination of target state and total time are investigated. It is suggested from the computational results that even when T is short, high-yield transitions into energetically-separated target states are possible through excitations skipping over more than one vibrational level at a time with intense fields including high overtones. Molecular orientation effect is studied based on an approximate model that molecules do not rotate during the laser pulse irradiation. It is found that in some cases optimal fields for the parallel orientation are sufficiently effective even when there are some minor deviations from parallel. Spatial laser-profile effect is also investigated assuming a pseudo-Gaussian profile. It is predicted that final yields for cases with long pulse durations are relatively insensitive to spatial position.