The laser-induced vibrational state-selectivity of product HF in photoassociation reaction H+F→HF is theoretically investigated by using the time-dependent quantum wave packet method. The population transfer process from the continuum state down to the bound vibrational states can be controlled by the driving laser. The effects of laser pulse parameters and the initial momentum of the two collision atoms on the vibrational population of the product HF are discussed in detail. Photodissociation accompanied with the photoassociation process is also described.
The laser-induced vibrational state-selectivity of product HF in photoassociation reaction H+F→HF is theoretically investigated by using the time-dependent quantum wave packet method. The population transfer process from the continuum state down to the bound vibrational states can be controlled by the driving laser. The effects of laser pulse parameters and the initial momentum of the two collision atoms on the vibrational population of the product HF are discussed in detail. Photodissociation accompanied with the photoassociation process is also described.
The photoassociation (PA) reactions of H + F → HF and D + F → DF are investigated by using the time-dependent quantum wave packet method. For each system, we consider four cases, where the target state is set to be ∣ ν = 16, 17, 18, 19〉, respectively. The effects of the initial collision momentum and laser parameters, including intensity, pulse duration, and frequency, on the final association probability are calculated and discussed. It is found that the PA probability for H + F → HF (∣ ν = 16, 17, 18〉) is significantly greater than that for D + F → DF (∣ ν = 16, 17, 18〉), while the PA probability to ∣ ν = 19〉 for the latter system is greater than the former one. This isotope effect has been connected with the Franck–Condon overlap integral between the target vibrational state and the collision continuum state.
Photoassociation via reverse ladder transition controlled by two and four laser pulses is investigated using the time-dependent quantum wave packet method. The calculated results show that the amplitudes of the pulses have an enormous effect on the target population and total yield of association. For the target state with a high energy level, the population of background states can reduce the state-selectivity. Although, the total yield of association is decreased, the four pulses can induce the population transferring to low vibrational levels, and the state-selectivity of the target state is high.
This paper aims at studying the time-dependent effects involved in the photoassociation reaction for a sample of cold alkali-metal atoms, within a two-channel model where the vibrational motion in the excited state is coupled by laser light to the continuum state describing two colliding atoms in the lowest triplet electronic state $(a{}^{3}{\ensuremath{\Sigma}}_{u}^{+}).$ Both photodissociation and photoassociation processes are considered at a time scale shorter than the radiative lifetime, so that spontaneous emission does not have to be considered. The characteristic times are then the vibrational period in the excited state, which for alkali-metal dimers can be estimated of the order of a few hundreds of picoseconds, and the Rabi period, depending upon the laser intensity. Numerical calculations using wave-packet propagation are performed for the coupling of the vibrational motion in the Cs21g(6s+6p3/2) and ${a}^{3}{\ensuremath{\Sigma}}_{u}^{+}(6s+6s)$ channels by a cw laser slightly red detuned relative to the D2 resonance line. The results show Rabi oscillations in the populations of the two channels during time intervals when the vibrational motion is stopped at the outer turning point. At intensities of $\ensuremath{\approx}250\mathrm{kW}{\mathrm{cm}}^{\ensuremath{-}2},$ a new characteristic time appears, a factor of 2 larger than the classical vibrational period, which corresponds to vibrational motion in the upper adiabatic potential created by the coupling. Such an effect modifies the scattering length for collisions in the lower state, and it clearly opens a possibility of control by tuning the laser intensity.
The selective control of photoassociation of Yb2 molecule is investigated in theory. Based on ab initio to rationalize Franck-Condon filtering, the optimal target states of photoassociation have been obtained. That correspond to vibrational transition levels from X1Σ+g to excited state (A1Σu+, B1Πu , C1Σu+, D1Πu) are v’=23, 50, 55, and 0, respectively. The proposed laser drive transitions to target states for association process at wavelength A1Σu+: 464.7nm, B1Πu: 373.1nm, C1Σu+: 361.8nm, D1Πu: 339.1nm are determined. By using quantum wave-packet dynamic methods, we calculated the yields with time evaluation for the selected target states. Interacting with a resonant laser pulse, the projections of time-dependent wave functions of initial states on the target vibrational eigenstates reflected the photoassociation yields of Yb2. For target A1Σu+, using gaussian pulse made the value of v’=23 up to 97% at 725fs. After a laser pulse, that the positive chirp promotes the yield of projection of vibrational states to increase, but the negative chirp inhibits it decrease. For D1Πu state, when laser intensity is 1.0×1014 W/cm2, not only the purity is high but also the yield is high reached 99% of target state v’=0 at 1570fs. That is to say, by changing the laser parameters and pulse shapes, it could much easier control the photochemical along our desired direction. These conditions will provide an important reference and suggest a scheme for a feasible photoassociation for further experimental and theoretical researches.
The selective control of photoassociation of Yb2 is investigated in theory. Based on ab initio to rationalize Franck–Condon filtering, the optimal target states of photoassociation have been obtained. The corresponding vibrational transitions from X1Σ+g to the excited state (A1Σu+, B1Πu, C1Σu+, and D1Πu) are v ′ = 23, 50, 55, and 0, respectively. By using quantum wave packet dynamic methods, we calculated the yields with time evaluation for the selected target states. The projections of time-dependent wave functions of initial states on the target vibrational eigenstates reflected the synthetic yields of Yb2. For target A1Σu+, we used Gaussian pulse to make the yield of v ′ = 23 up to 97% at 725 fs. After a laser pulse, the positive chirp promoted the yield of vibrational states to increase, but the negative chirp inhibited its decrease. For the D1Πu state, when laser intensity is 1.0 × 1014 W/cm2, the purity and yield of target state v ′ = 0 reached the maximum at 1350 fs. That is to say, changing the laser parameters and pulse shapes could control the photochemical reaction along our desired direction. These conditions will provide an important reference and suggest a scheme for a feasible photoassociation of further experimental and theoretical research studies. Current study may promote an important step toward the realization of highly accurate quantum manipulation and material synthesis.