1. Ivan Janeček, Daniel Hrivňák, and René Kalus Department of Physics, University of Ostrava, Ostrava, Czech Republic Supported by the Grant Agency of the Czech Republic (grant. no. 203/02/1204) Fragmentation Dynamics of Singly Ionised Homogeneous Rare Gas Trimers from Adiabatic States Ivan Janeček, Daniel Hrivňák, and René Kalus Department of Physics, University of Ostrava, Ostrava, Czech Republic Supported by the Grant Agency of the Czech Republic (grant. no. 203/02/1204) THEORY: Hemiquantal dynamics and extended DIM method Neutral diatoms: empirical data Ar2 – R. A. Aziz, J. Chem. Phys. 99 (1993), 4518. Singly charged diatoms: computed ab initio by I. Paidarová and F. X. Gadéa (1996) The spin-orbit constant used is of empirical origin. Simulation: Fragmentation of the Rg 3 + cluster after sudden ionisation from energy level E i. A neutral trimer in the static equilibrium configuration (equilateral triangle) is vibrationally excited. Now, the trimer is suddenly ionised to energy level E i from the cation trimer energy spectrum. After MC equilibration the heated cluster has a random configuration different from the initial one (a distorted triangle). The molecular dynamics runs up to 10 5 fs. As soon as a cluster decay is indicated, the calculations is stopped. PRAHA OSTRAVA Model: DIM + SO + ID-ID * The initial state of the neutral cluster: equilibrium geometry, zero angular momentum, nonzero vibrational kinetic energy E k. The initial state of the ion cluster: energy level E i, where i = 1, 3, 5, 7, 9, 11, 13, 15, 17 (double degeneration). * From diabatic decay simulations we know that the spin orbit coupling has major influence on the time of decay, wherefore DIM model with the inclusion of the SO coupling is used, ID-ID interaction does not seem to be relevant in this case. Results: Fragmentation of Xe 3 + cluster after sudden ionisation Field of study: Rare gas cation trimers of Ar, Kr, Xe (= Rg) with initial kinetic energy E k from the zero point vibration energy E 0 to the dissociation limit (DL) energy E dl (dissociation of the Rg 3 to Rg 2 and Rg). At present trimers Rg 3 + are studied. However, fragmentation of larger Rg n + clusters (n>3) can also be computed. We have computed 2000 trajectories for each energy level. For initial heating with E k = E 0 = 0.0038 eV we have observed no decay from either energy level up to time 100 ps. In the left figure the histogram (in form of the point graph) of the time of decay is plotted for E k = E dl = 0.0487 eV. The y-scale is correct for basic energy level only. Curves for higher adiabatic levels are shifted along the vertical axis. The main way of the decay is a fragmentation to a dimer and a single atom. One can observe quick decay from the ground state and also from E11 level, where also the fragmentation to single atoms is observed (channel 3). On the other hand, no decay has been observed for E15 level. In the right picture one can see summary of some mean values. Bottom contour plots show the potential energy surfaces of Xe 3 + for levels E11 (left) and E15 (right) as a function of xy-coordinates of the third atom Xe for fixed positions of the two remaining atoms (1 and 2). Their distance R 12 = 4.45 angstrem, which is a mean value of the shortest side of Xe 3 triangle after the equilibration phase. Small points correspond to Xe 3 + configurations obtained after this phase (These configurations are initial configuration for molecular dynamics on ion cluster). The red line is an approximate “lower boundary” of the configurations. Atoms 1 and 2 are situated on axis x and have equivalent distance from axis y. Coloured circles at axes show positions of the atoms in configuration corresponding to the potential energy surface minimum (PES E11- equilateral triangle, PES E15 – equilateral triangle and linear trimer). In the case of the initial adiabatic state E15 no decay has been observed for any initial configurations, in the case of the initial adiabatic state E11, on the contrary, a frequent fragmentation has been observed, the green points relate to the initial configuration without decay observed. For illustration, sections for x 3 = 0 are plotted for all the levels in the middle graph. Hemiquantal, mean-field dynamics (HWD) [1] and recently developed extended diatomics-in-molecules (DIM) [2, 3] models of intra-cluster interactions with the inclusion of the spin-orbit coupling (DIM +SO) [4] and the most important three-body forces induced dipole – induced dipole interactions (DIM +SO + ID-ID) [5] are used to study fragmentation of argon, krypton and xenon trimer cations after a sudden ionization of respective vibrationally excited neutral trimers. [1] M. Amarouche, F. X.Gadea, J. Durup, Chem. Phys. 130 (1989) 145-157 [2] F. O. Ellison, J. Am. Chem. Soc. 85 (1963), 3540. [3] P. J. Kuntz & J. Valldorf, Z. Phys. D (1987), 8, 195. [4] J. S. Cohen and B. Schneider, J. Chem. Phys. 64 (1974) 3230 [5] M. Amarouche et al., J. Chem. Phys. 88 (1988) 1010].