Ultrafast laser control of ionic-bond formation: ClF in argon solids

The formation of the two ionic products of Cl+F- versus Arn+F- is controlled by variation of the time delay between two ultrafast UV pulses. The Arn+F- exciplex is characterized by a fluorescence band at 355 nm and the Cl+F- product by the D-' emission at 420 nm. In this Tannor-Kosloff-Rice control scheme, the pump pulse dissociates ClF in a solid argon matrix. During the early dynamics in the matrix cage the F fragments have sufficient kinetic energy to closely approach the Ar atoms. Here a control pulse, which is delayed by typically 3 ps, induces the ionic bond Arn+F-. Energy loss by collisions with the cage leads to recombination and vibrational relaxation in the B state of ClF. A control pulse delayed by 30-100 ps leads to exclusive formation of the ionic bond Cl+F-. A switching contrast better than 1 to 10 can be achieved in both directions. The control scheme makes use of the time scale of vibrational relaxation. By femtosecond pump-probe spectroscopy we show the wave packet oscillations from the recombination dynamics in the cage lasting for 2 ps and determine the subsequent decay of vibrational energy. (C) 2001 American Institute of Physics.