Effect of the spin-orbit coupling in the dissociation dynamics of rare-gas ionic trimers

Abstract

A dynamical model combining an extended diatomics-in-molecules approach with the inclusion of the spin-orbit coupling and the mean-field dynamics method has been developed for rare-gas cluster cations, Rg + n , and employed in simulations of the photodissociation dynamics of argon, krypton, and xenon singly charged trimers. As the first step, total kinetic energies deposited in the photofragments are calculated for all the three rare gases and for a wide range of photon energies, and compared with available experimental data. A very good agreement between experiment and theory is reached, including a plausible theoretical explanation for an abrupt change in the total kinetic energy of photofragments at about 2.5 eV of photon energy, which was recently observed experimentally for Xe + 3 (and also, but less clearly for Ar + 3 ).

Photodissociation dynamics of ionic argon pentamer

“…In this case, only monomers are produced in experiments [16] with a bimodal kinetic energy distribution (fast and slow fragments) both for neutrals and for ions. Our earlier [6,13,[17][18][19][20] as well as recent [14,15] theoretical simulations have nicely reproduced these experimental findings and showed that, in visible excitation, the trimer, initially almost linear and symmetric, mainly explodes leaving the central atom to rest in the center-of-mass. Interestingly, for the higher photon energies, the ions are produced in the high fine-structure state [15] corroborating the experimental findings [16].…”

“…Our earlier [6,13,[17][18][19][20] as well as recent [14,15] theoretical simulations have nicely reproduced these experimental findings and showed that, in visible excitation, the trimer, initially almost linear and symmetric, mainly explodes leaving the central atom to rest in the center-of-mass. Interestingly, for the higher photon energies, the ions are produced in the high fine-structure state [15] corroborating the experimental findings [16]. It should be noticed that, in a very recent experiment on Ar + 2 and Ar + 3 [8], the velocity vectors of all fragments have been collected in coincidence thanks to the development of sophisticated multicoincidence techniques.…”

“…As discussed already in an earlier study [15], the electronic states of the rare-gas clusters cations available within the diatomics-inmolecules modeling split up into two groups if the spin-orbit coupling is included: a group of states asymptotically correlating to 2 P 3/2 atomic ions (in general, lower 2/3 of the electronic states, and specifically for Ar + 3 , the electronic ground state and five lowest excited states) and another group correlating asymptotically to 2 P 1/2 atomic ions (remaining 1/3 of the electronic states, i.e., the highest three excited states available for Ar + 3 within the DIM+SO model). While the two groups interact only weakly with each other, non-negligible nonadiabatic couplings are observed between the states belonging to each particular group.…”

“…In this work we use the diatomic curves for Ar + 2 taken from ab initio calculations [28], a state-of-the-art semiempirical potential for neutral Ar 2 [29], and the spin-orbit coupling constant extracted from experimental data on the splitting between the 2 P 1/2 and 2 P 3/2 fine-structure states of Ar + [30]. The DIM+SO model used in this work has many times been tested successfully against available experimental data on small and medium-size argon clusters, including their structures and energetics [6,31], photoabsorption [6], and non-adiabatic dynamics [14,15,32], and can, thus, be considered well established for the description of intra-cluster interactions in these clusters.…”

“…They include sampling of the initial cluster configuration, modeling the photon absorption and the ensuing non-adiabatic dynamics spanning a broad manifold of electronic states as well as nuclear degrees of freedom, and analyzing the fragments. For example, the photodissociation of ionic rare-gas trimers has been thoroughly investigated [13][14][15] because the trimer is mainly the chromophoric core in larger clusters. In this case, only monomers are produced in experiments [16] with a bimodal kinetic energy distribution (fast and slow fragments) both for neutrals and for ions.…”