Using the time-dependent quantum wave packet method, the photoassociation (PA) processes of He + H + ! HeH + and He + D + ! HeD + , driven by the sin 2 -shaped femtosecond laser pulse in the electronic ground state, including multiphoton transitions and dissociations, are investigated for a wide range of initial collision momenta spanning from 1 to 4 a.u. (or for the collision energy roughly in the ranges of 0.0090.148 eV and 0.0060.089 eV for HeH + and HeD + systems, respectively). It is found that, at some collision momenta, multiphoton transitions to deeply bound states are inevitable to occur and can greatly decrease the PA probability of the target state that selected is the vibrational state v = 6. For the dissociation process, the higher-order (two-and three-photon) dissociations, measured from the target state, tend to be significant at relative high collision energies, which implies that abovethreshold dissociations may also be an important loss mechanism in the PA process.In addition, it is also shown that the higher-order dissociation is much stronger for HeH + systems than that for HeD + systems at a given collision momentum, and could be enhanced by the strong transitions among deeply bound states.above-threshold dissociations, dissociations, multiphoton transitions, photoassociation, time-dependent quantum wave packet method | INTRODUCTIONAs a rapidly developing research field, preparations of cold and ultracold molecules have attracted significant attention in recent years. [1][2][3][4][5][6] These produced molecules, which present strong quantal features, can be used to explore various novel phenomena and dynamic mechanisms, such as the quantum fluid [7] and the topological superfluid phase. [8] Furthermore, these molecules are also important in the measurement of fundamental physical constants, [9][10][11] and in the field of molecular spectroscopy [12] and ultracold chemistry. [13,14] Among myriad routes to prepare ultracold molecules, photoassociation (PA) emerges as an efficient method, which allows us to directly synthesize ultracold molecules, with the interaction of laser field, from an assembly of laser-cooled atoms. [1,2] In a general PA process, a pair of ultracold atoms colliding in the ground electronic state is firstly associated into vibrational levels of the excited electronic state by absorbing one photon. Then, it is followed a stabilization step by either the spontaneous or stimulated emission, which enables us to obtain ultracold groundstate molecules. In the past few years, a burst of PA schemes have been seen, such as chirped pulses, [15,16] asymmetric pulses (or a train of these pulses), [17,18] electric-magnetic fields, [19] pump-dump shames (or a combination of these shames with chirped pulses), [20][21][22] and so on. Recently, we found that the molecular alignment occurs in the pump-dump PA process and can also be used to control the PA process. [23] In addition, for heteronuclear molecular systems with considerable permanent dipole moments, such as He + H + , [24,25] H +...

Atom-atom-anion three-body recombination (TBR) in mixed 4He and xLi− (x = 6 or 7) is investigated in the adiabatic hyperspherical representation by quantum mechanically solving the Schrödinger equation. The distributions of product states following these TBR processes are found to be relatively different for the two systems when the collision energy is less than roughly 0.6 mK × kB or 0.3 mK × kB for 4He4He6Li− and 4He4He7Li− systems, respectively, with kB being the Boltzmann constant. For 4He4He6Li− systems, the rate of recombination into (v=0) l = 04He6Li− molecular anions is the largest with v and l denoting the rovibrational quantum numbers, while the TBR rate that leads to the formation of l = 14He6Li− molecular anions is a little smaller than that of neutral 4He2 molecules. For 4He4He7Li− systems, neutral 4He2 molecules tend to be the most products, following the yields of l = 0 and 1 4He7Li− molecular anions. However, in spite of these distinctly different distributions, the products of molecular anions, the sum of l = 0 and 1 4HexLi− products, are relatively larger than that of neutral 4He2 molecules for both the two systems.