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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 +...
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 role of rotational degree of freedom in calculations of photoassociation (PA) and the accompanying phenomena, that is, multiphoton transitions and above-threshold dissociations (PA-ATDs), of HeH + systems is investigated by comparing the numerical results of the one-dimensional (1D) and three-dimensional (3D) models in the framework of the time-dependent quantum wave packet method. It was found that the PA probability of the target state predicted by the 3D model is much smaller than that predicted by the 1D model. In addition, as the bound energies of interaction potential can be shifted by the inclusion of the rotational degree of freedom, the amplitude and frequency of optimized laser pulses obtained based on the 1D model should be changed to some extent to obtain maximal PA probability of the target state in realistic systems. The multiphoton transitions in the 3D case tend to be much easier to be excited. The variational behaviors of the PA-ATD probability vs the initial relative momentum of the two colliding particles, calculated in the 3D model using the optimized laser pulses obtained based on the 1D and 3D models, are found to be nearly coincident with each other, which implies that the continuum-continuum transitions from the initial wave packet tend to be the major dynamics in the PA-ATD process.
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.
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