Quantum control of iodine photodissociation in gas phase and condensed phase environments.

摘要

Quantum control of I₂ photodissociation using coherent radiation was demonstrated in both gas and condensed phase environments. Weak-field optimal control theory was applied in both systems to calculate the electric field that effects localization of the vibrational wavefunction on an excited electronic surface. Two factors which affect the degree of control were investigated in the gas phase system. The weak field control equation was solved at temperatures higher than the vibrational temperature ($Qv$) of I₂ in order to examine qualitatitvely the effect of a statistical mixture of states on the control. As the temperature increases, the results indicate decreasing control due to the inhomogeneous dynamical effect of the different vibrational states. To elucidate the role played by the frequency-time profile of the laser field, the optimal field was calculated for two types of target, a molecular “cannon” which consists of a minimum uncertainty wavefunction with outgoing momentum centered at or near the dissociative region of the potential, and the “reflectron” which is a bound wavepacket that has incoming momentum. The results of the control study on both targets highlight the importance of chirped pulses in the achievement of vibrational localization. Furthermore, these results agree with other theoretical and experimental observations made on a similar physical system.; Control of I₂ embedded in solid Ar matrix was implemented using a time-dependent Hartree factorization in which the I-I vibrational motion was calculated quantum mechanically while the dynamics of the lattice atoms were given classical treatment. This method allows the calculation of optimal fields for longer times and with a greater flexibility in the choice of target relative to a previous method put forward in an earlier work which utilized semiclassical techniques to calculate the I-I vibrational dynamics. The thermal dependence of control was investigated by calculating the optimal field at temperatures below the $Qv$ of I₂. As expected, control is degraded as temperature is increased due to the more rapidly fluctuating environment provided by the lattice as more thermal energy becomes available. The effect of molecular rotation was shown to be minimal at the temperatures considered in this study.