This work explores the vibrational state-selective photoassociation (PA) in the ground state of the HX (X = F, Cl, I) molecule by solving the time-dependent Schrödinger equation. For the three systems, the vibrational level of [Formula: see text] is set to be the target state and the PA probability of the target state is calculated and compared by considering different initial collision momentums. It is found that the PA probabilities are in accordance with Franck–Condon overlap integral for the HI and HCl systems, but it is not the case for the HF system. Moreover, for the HF system, it is shown that the PA probability of the target state is largest and the multiphoton transition is more likely to occur.

The ultracold state-to-state chemistry for three-body recombination (TBR) in realistic systems recently could be experimentally investigated with full quantum state resolution. However, many detected phenomena remain challenging to be explored and explained from the theoretical viewpoints because this generally requires computational powers beyond the state-of-the-art. Here, the product-state distributions after TBR of 3He2-alkaline-earth-metal systems, i.e. after the processes 3He+3He+X→3HeX+3He with X being 9Be, 24Mg, 40Ca, 88Sr, or 138Ba, in the zero-collision-energy limit are theoretically studied. Two propensity rules for the distribution of the products found in current experiments have been checked, and the mechanism underlying these product-state distributions is explored. Particularly, two main intriguing transition pathways are identified, which may be responsible for the nonlinear distribution of the products versus their rotational quantum number. In addition, the total TBR rates of these systems are also accounted for by the joint effects of major adiabatic potential energies and relevant nonadiabatic couplings.

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 +...

The atom-atom-ion three-body recombination (TBR) of mixed He and X (X = H or D) systems is investigated by solving the Schrödinger equation using the adiabatic hyperspherical representation method. It is shown that the dominant products after a TBR in the ultracold limit (E ≤ 0.1 mK × k) are different for the two systems. For the HeHeH system, the rate of TBR into the HeH ion is nearly two orders of magnitude larger than that of TBR into the neutral He molecule. In contrast, the yield of He is a little higher than that of HeD for the HeHeD system. Furthermore, since the adiabatic potentials become more attractive and the nonadiabatic couplings become much stronger by substituting D for H in the HeHeH system, the total TBR rate for the HeHeD system is nearly two orders of magnitude larger than that for the HeHeH system.