Laser control of molecular photodissociation with use of the complete reflection phenomenon

A new idea of controlling molecular photodissociation branching by a statio nary laser field is proposed by utilizing the unusual intriguing quantum-me chanical phenomenon of complete reflection. By introducing the Floquet (or dressed) state formalism, we can artificially create potential curve crossi ngs, which can be used to control molecular processes. Our control scheme p resented here is summarized as follows. First, we prepare an appropriate vi brationally excited state in the ground electronic state, and at the same t ime by applying a stationary laser field of the frequency omega we create t wo nonadiabatic tunneling (NT) type curve crossings between the ground elec tronic bound state shifted up by one photon energy (h) over bar omega and t he excited electronic state with two dissociative channels. In the NT-type of curve crossing where the two diabatic potential curves cross with opposi te signs of slopes, it is known that the complete reflection phenomenon occ urs at certain discrete energies. By adjusting the laser frequency to satis fy the complete reflection condition at the NT type curve crossing in one c hannel, the complete dissociation into the other channel can be realized. B y taking one- and two-dimensional models which mimic the HOD molecule and u sing a wave packet propagation method, it is numerically demonstrated that a molecule can be dissociated into any desired channel selectively. Selecti ve dissociation can be realized even into such a channel that cannot be ach ieved in the ordinary photodissociation because of a potential barrier in t he excited electronic state. (C) 2000 American Institute of Physics. [S0021 -9606(00)00639-5].