Spin-orbit coupling in the dissociative excitation of alkali atoms at the surface of rare gas clusters: A theoretical study

International audienceWe analyze the role of the spin-orbit (SO) coupling in the dissociative dynamics of excited alkali atoms at the surface of small rare gas clusters. The electronic structure of the whole system is deduced from a one-electron model based on core polarization pseudo-potentials. It allows us to obtain in the same footing the energy, forces, and non-adiabatic couplings used to simulate the dynamics by means of a surface hopping method. The fine structure state population is analyzed by considering the relative magnitude of the SO coupling ξ, with respect to the spin-free potential energy. We identify three regimes of ξ-values leading to different evolution of adiabatic state population after excitation of the system in the uppermost state of the lowest np 2P shell. For sufficiently small ξ, the final population of the J=12 atomic states, P12, grows up linearly from P12=13 at ξ = 0 after a diabatic dynamics. For large values of ξ, we observe a rather adiabatic dynamics with P12 decreasing as ξ increases. For intermediate values of ξ, the coupling is extremely efficient and a complete transfer of population is observed for the set of parameters associated to NaAr3 and NaAr4 clusters

RASPT2 Analysis of the F – (H 2 O) n =1–7 and OH – (H 2 O) n =1–7 CTTS States

International audienceWe analyze the electronic structure of the lowest excited states of the F–(H2O)n=1–7 and OH–(H2O)n=1–7 anionic clusters in the framework of RASPT2 theory. At the ground-state geometry, these clusters can bind the excess electron in the first excited singlet and triplet states for n ≥ 3 for F– and n ≥ 2 for OH–. The geometry relaxation of the F–(H2O)n=1–7 clusters in their lowest-energy triplet state produces two series of minima. A first series is made of a F radical weakly bound to a negatively charged water cluster to form F-(H2O)n–. A second series associated with hydrogen transfer from a water molecule to the fluorine atom is built on a HF molecule and a OH radical bound to a negatively charged water cluster to form OH-HF-(H2O)n−1–. This second series provides the lowest-energy isomers of F–(H2O)n for the excited state. These two series of minima are inherited from the neutral fluorine water cluster structure only weakly perturbed by the excess electron. They are similar to the OH–(H2O)n isomers obtained for the lowest-energy triplet state, which are also made of a neutral OH radical inserted in the water molecule network of a (H2O)n– cluster. For all of these clusters in the lowest-energy excited state, the excess electron is localized outside of the cluster near unbound hydrogen atoms. Its binding energy is well correlated to the electric dipole of the cluster, and a lower limit of 4.1 D is necessary to bind it to the cluster. The two series of F–(H2O)n isomers offer two very different routes for geminate recombination observed in water solutions. Our calculation suggests that the recombination takes place with the OH radical left after hydrogen transfer rather than with the F radical

Lightness effects in Delboeuf and Ebbinghaus size-contrast illusions

We examined lightness effects observed in Delboeuf and Ebbinghaus size-contrast illusions. Results of four experiments are reported. Experiment 1 was conducted with Delboeuf- like stimuli and shows that the disk that appears bigger appears either lighter or darker than the disk that appears smaller, depending on the contrast polarity between disks and background. Experiment 2 shows that the direction of these lightness effects is not influenced by the lumi- nance of the size-contrast inducers. Experiment 3 shows that a similar lightness effect is also observed in modified Ebbinghaus size-contrast displays. Experiment 4 tested the presence of the size-contrast illusion in the stimuli used in experiments 2 and 3