STATE-SELECTIVE CONTROL FOR VIBRATIONAL-EXCITATION AND DISSOCIATION OF DIATOMIC-MOLECULES WITH SHAPED ULTRASHORT INFRARED-LASER PULSES

Ultrafast state-selective dynamics of diatomic molecules in the electr onic ground state under the control of infrared picosecond and femtose cond shaped laser pulses is investigated for the discrete vibrational bound states and for the dissociative continuum states. Quantum dynami cs in a classical laser field is simulated for a one-dimensional nonro tating dissociative Morse oscillator, representing the local OH bond i n the H2O and HOD molecules. Computer simulations are based on two app roaches - exact treatment by the time-dependent Schrodinger equation a nd approximate treatment by integro-differential equations for the pro bability amplitudes of the bound states only. Combination of these two approaches is useful to reveal mechanisms underlying selective excita tion of the continuum states and above-threshold dissociation in a sin gle electronic state and for designing optimal laser fields to control selective preparation of the high-lying bound states and the continuu m states. Optimal laser fields can be designed to yield almost 100% se lective preparation of any prescribed bound state, including those clo se to the dissociation threshold. State-selective preparation of the h ighest bound state may be accompanied by the appearance of a quasi-bou nd molecular state in the continuum with the kinetic energy of the fra gments being close to zero. The respective above-threshold dissociatio n spectrum contains an additional, zero-order peak. The laser-induced dissociation from selectively prepared high-lying bound states is show n to be very efficient, with the dissociation probability approaching the maximal value. Flexible tools of state-selective laser control are developed which enable one to achieve selective control of the dissoc iation spectra resulting in time-selective and space-selective control of the dissociation fragments. (C) 1996 American Institute of Physics .