Photoassociation Dynamics Of The Polar Diatomic Molecule In The Femtosecond Laser Fields

In a dilute gas, a free→bound transition can be achieved by absorption or emission of photons to yield molecule. Photoassociation process is much less well-understood than its reversed process photodissociation. Only recently there has been an increasing interest in photoassociation reactions which was stimulated by new experiments involving collisions of laser-cooled atoms. In particular, the observation and control of photoassociation dynamics by using short pulse techniques, as the extension of fem-tochemistry to binary reactions, are still at its infancy and remain a challenge. Our aim of the present work is to investigate the photoassociation dynamics of the polar diatomic molecules in the ultra-fast laser fields. Quantum wave packet method used for solving the time-dependent Schrodinger equation is implemented for revealing the reactive dynamics process.First, we theoretically investigate the vibrationally state-selective photoassociation by infrared sub-picosecond laser pulse. The laser-assisted collision reaction I + H→HI is simulated to reveal the effects of the laser pulse parameters and the relative collision momentum on the state-selective population of the product molecule. Moreover, the multiphoton association reaction He+H~+→HeH~+ in the electronic ground state is investigated. The multiphoton transition takes place via intermediate state, and the transfer probability is determined by the collision energy and the intermediate state. The collision pairs He+H~+ in continuum state can transfer into v= 0 state to yield the stable molecules HeH~+ via emission of two or three photons.Second, the photoassociation reactions H+D~+ and H~++D induced by the one-and two-color laser pulses are theoretically studied using the time-dependent quantum wave packet method. The photoassociation reactions occur through two channels: (i) H(1S)+D~+→HD~+, and (ii) H~++D(1S)→HD~+. The reaction probability through channel (ii) is higher than that through channel (i). The populations of the products H~++D and HD~+ can be controlled by the laser pulses. The two-color laser pulses can more efficiently lower the dissociation probability and therefore enhance the yield ratio of the product HD~+ than the one-color laser pulse. At the ultracold temperature, the two chirped pulse scheme is employed. The first pulse is used to induce the acceleration of the collision pairs, and the second one enhances the yield ratio of HD~+. The population of the product depends on the chirp rate of the first pulse.Third, the photoassociation and photodissociation processes in laser-assisted collision H+Cl~+ are simulated. The theoretical calculations show the dissociation probability and the photofragment branching ratio of the product HCl~+ depend on the yield ratio of association. The kinetic energy spectra of the dissociated fragments derived from high vibrational state are wider than those from low vibrational state.