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.