Daniel Hrivňák, Ivan Janeček 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 Ionized Homogeneous Rare Gas Trimers Daniel Hrivňák, Ivan Janeček 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 with the whole DIM basis (HWD) M. Amarouche, F. X.Gadea, J. Durup, Chem. Phys. 130 (1989) multi-electronic-state molecular dynamics DIM Method F. O. Ellison, J. Am. Chem. Soc. 85 (1963), P. J. Kuntz & J. Valldorf, Z. Phys. D (1987), 8, 195. Diatomic inputs Neutral diatoms: empirical data Ar2 – R. A. Aziz, J. Chem. Phys. 99 (1993), Singly charged diatoms: computed ab initio by I. Paidarová and F. X. Gadéa (1996) The spin-orbit constant used is of empirical origin. DIM + SO [M. Amarouche et al., J. Chem. Phys. 88 (1988) 1010] The DIM model with inclusion of the spin-orbit coupling. [J. S. Cohen and B. Schneider, J. Chem. Phys. 64 (1974) 3230]. DIM + SO + ID-ID [M. Amarouche et al., J. Chem. Phys. 88 (1988) 1010]. Inclusion of the most important three-body forces corresponding to the interaction of two atomic dipoles induced by a positive charge localized on a third atom. DIM extensions SIMULATION I: Fragmentation of the Rg 3 + cluster after sudden ionisation A neutral trimer in static equilibrium configuration is vibrationally excited. Now, the trimer is suddenly ionised. (Red colour indicates positive charge localized on an atom in case diabatic Ionisation). After dynamic equilibrisation the heated cluster has a random configuration different from initial one. The molecular dynamics continues up to 10 5 fs. In case of a cluster decay indication the dynamics is stopped. Results 1: Role of spin-orbit coupling (SO), induced dipole - induced dipole interaction (ID-ID) and initial vibrational excitation (E v ) in Ar3+ decay Results 2: Comparison Ar3+, Kr3+ and Xe3+ decay. Initial heating of clusters to vibrational energy E V shortens time of decay, especially for disociation limit energy E dis, which is energy released in decay of neutral trimer on dimer and monomer. Energy E 0 represent estimate of basic quantum vibration (“zero vibration”). Table of average values Average values: - electric charge single Ar emitted, E KER – kinetic energy released, E vib, E rot, E tr – vibration, rotation and translation energy (REM – Ar2 remainder, EMIT – Ar emitted) * A. Bastida, N. Halberdstat, J.A. Beswick, F.X. Gadéa, U. Buck, R. Galonska, C. Lauenstein, Chem. Phys. Lett. 249 (1996)1-6 The spin orbit coupling has major influence on decay. Time of decay is higher if SO is on. On the contrary a role of induced dipole – induced dipole interaction is not relevant. For E v =E 0 none or sporadic fragmentations of Kr and Xe trimer ions are observed up to 10 5 fs. More frequent decay was found for higher initial vibrational excitation. For E v = E dis a fragmentation of population of the Ar 3 + is very quick in comparison with Kr and Xe cases. PRAHA OSTRAVA SIMULATION II: Photodissociation of the vibrationally excited Rg 3 + cluster Stable configuration of the Rg 3 + on the basic electronic level. Vibrationally excited Rg 3 + cluster on the basic electronic level. The same configuration as previous one. Cluster is excited to the higher electronic level. h Photon absorption Heating Dissociation Cluster is decayed to the single atoms. Xenon SO constant = eV E( 2 P 1/2 ) – E( 2 P 3/2 ) = eV D 0 (Xe 3 + ) = eV 1 Experiment: Haberland, Hofmann, and Issendorff, J. Chem. Phys. 103, 3450 (1995). A general fragmentation pattern from experiment 1, confirmed by our theoretical calculations at low temperatures: the middle atom obtains only a small velocity, two remaining outer atoms gain high velocities in opposite directions. The positive charge is usually localized on one of the fast outer atoms (the asymmetric fragmentation), but localization of the charge on the slow middle atom (the symmetric case) is observed too. An essential role in the theoretical and experimental results plays the spin- orbit splitting of the Rg+ ion to the two states 2 P 1/2 and 2 P 3/2 with some energetical gap. Argon SO constant = eV E( 2 P 1/2 ) – E( 2 P 3/2 ) = eV D 0 (Ar 3 + ) = eV