Laser Physics Letters

Above-threshold dissociation occurring during photoassociation

Yong‐Chang Han

Published Nov 23, 2017• 5 citations

Abstract

Abstract Using the quantum wave-packet method, we investigated the photoassociation (PA) processes of H + + He → HeH + in the ground electronic state (X 1 Σ g + ). Two cases are considered where the target vibrational state selected is v = 4 and 8, respectively. It is found (for the first time) that above-threshold dissociation (ATD) occurs alongside the PA process (PA-ATD). ATD dissociation can be the major loss mechanism for the PA process. Compared with the direct dissociation from a given vibrational state and continuum–continuum transitions to the same final energy, the overall PA-ATD process is enhanced in comparison to individual contributions due to correlations. The one-photon dissociation from the target vibrational state, the ATD signals from two-photon dissociation and the higher-order (three- and four-photon) dissociations are the results of different mechanisms.

DOI: 10.1088/1612-202x/aa9317

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Laser Physics Letters

Above-threshold dissociation occurring during photoassociation

Yong‐Chang Han

Published Nov 23, 2017• 5 citations

Publisher

Abstract

DOI: 10.1088/1612-202x/aa9317

Related papers

Comparative study of the photoassociation reaction of He + X+→ HeX+ (X = H, D): Including multiphoton transitions and dissociations

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We consider the process of photoassociation (PA) that occurs when a pair of colliding atoms interacts with a photon, thereby making a transition from the two-atom continuum to a bound molecular state. Such free-bound transitions are described by quantizing the molecule's dissociation continuum, and coupling each of these quasicontinuum (QC) levels to a similarly discrete molecular level. The correct free-atom results are recovered no later than at the end of a given calculation by taking the limit as the QC spacing tends to zero. From the quasicontinuum model, we are led to adapt the few-level and second-quantization methods of photon optics to analyze free-bound transitions. In particular, we establish the PA density parameter as nearly identical to the phase-space parameter as a Bose-Einstein condensate (BEC), illustrate the near-unit efficiency of one- and two-color photoassociation of a BEC, and develop coherent atom-molecule transitions as the matter optics version of second-harmonic generated photons. ^We consider the process of photoassociation (PA) that occurs when a pair of colliding atoms interacts with a photon, thereby making a transition from the two-atom continuum to a bound molecular state. Such free-bound transitions are described by quantizing the molecule's dissociation continuum, and coupling each of these quasicontinuum (QC) levels to a similarly discrete molecular level. The correct free-atom results are recovered no later than at the end of a given calculation by taking the limit as the QC spacing tends to zero. From the quasicontinuum model, we are led to adapt the few-level and second-quantization methods of photon optics to analyze free-bound transitions. In particular, we establish the PA density parameter as nearly identical to the phase-space parameter as a Bose-Einstein condensate (BEC), illustrate the near-unit efficiency of one- and two-color photoassociation of a BEC, and develop coherent atom-molecule transitions as the matter optics version of second-harmonic generated photons. ^

Oct 1, 19991 citation

^{2}

S)+

{\mathrm{Na}}^{\mathrm{*}}

^{2}

{\mathit{P}}_{3/2}

) dissociation limit have been obtained by monitoring an enhanced

{\mathrm{Na}}_{2}^{+}

ion signal. We propose the use of pump-probe techniques to study the dynamics of the ionization process. At very large distances (typically 70 a.u.) two colliding Na atoms absorb a photon and form a coherent vibrational wave packet. We follow the packet in time and probe two possible mechanisms that are proposed to yield molecular ions: photoionization, where the second photon is absorbed at a small internuclear distance R directly ionizing the molecule, and associative ionization with excitation at intermediate R to the nuclear continuum of a doubly excited state followed by a half collision and autoionization at small R. The latter event can also lead to dissociation of the complex. The two mechanisms lead to distinct differences in the ion signals as a function of delay time between the pump and the probe pulses. Estimates of the ion rates to be expected in actual pump-probe experiments are given, which tend to favor the autoionization mechanism as the dominant reaction path.