Dynamics of excited rare gas cluster cations 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. 203/04/2146) Method for numerical simulation: Hemiquantal dynamics [1] EXCITATION After MC equilibration the heated cluster had a random configuration different from the initial one (a distorted triangle). In the next step the trimer was suddenly ionised to energy level Ei from the cation trimer energy spectrum. This state is initial state for MD simulations. For each energy level we studied the count of fragmentations from 2000 trajectories up to 10 5 fs of real process time. PRAHA OSTRAVA Fragmentation of rare gas trimers in adiabatic states after sudden ionisation The first column of the figures on the left represent the histograms of the time of decay for argon, krypton and xenon. Curves for adiabatic levels higher than basic level are shifted along the vertical axis (blue lines mark zero value). The second column contain mosaics of quaternions of the graphs which show numbers of decays and mean values of the decay time, electric charge of evaporated single atom and kinetic energy of released atoms. Model with initial vibrational excitation to E k = E 0 For argon trimers a frequent and quick fragmentation has been observed (see figure on the left) from each energy level with exception of E13 level (no decay) and the nearest neighbouring levels (sporadic and slow decay). For krypton trimers we observe frequent fragmentation from the first three levels. For level E7 and for level E13 and higher no decay has been observed. In case of xenon trimers a fragmentation has been detected only from basic level up to time 100 ps, thus for next studies model with higher heating of the neutral clusters was used. Model with initial vibrational excitation to E k = E dis For argon trimers the massive decay can be observed from each energy level. From level E15 and E17 even the fragmentation to the single atoms has been detected. Maximal mean time of decay for standard channel (decay to dimer and single atom) was found for E15. For krypton and xenon trimers one can see similar situation (decay for all levels with exception E15 for xenon), but the mean decay time is longer, fragmentation to the single atoms has been detected from level E11 and E17, and mean time of decay (as function of level number) has two local maxima for level E9 and E15. Interesting result of our studies is stability of trimer cation (or existence of long living state) in some adiabatic states.* *Private communication: Metastable decay (time of decay about 40μs) of the krypton trimer cations was observed in experiment [K.Gluch et al, J.Chem Phys. 120 (2004), 2686] Model: DIM ● diatomics-in-molecules [2, 3] models of intra-cluster interactions + SO ● inclusion of the spin-orbit coupling [4] + ID-ID ● inclusion of three-body induced dipole – induced dipole interactions [5] [1] M. Amarouche, F. X.Gadea, J. Durup, Chem. Phys. 130 (1989) [2] F. O. Ellison, J. Am. Chem. Soc. 85 (1963), [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]. Ar 3 Kr 3 Xe 3 IONISATION FRAGMENTATION Monte Carlo Simulation Molecular Dynamics Simulation Neutral trimers in the static equilibrium configuration (equilateral triangle) were vibrationally excited to determined energy. In our models its value was from the zero point energy E 0 to the dissociation limit energy E dis. The values of these energies for argon, krypton and xenon are presented in the table together with the global minimum energy E min. Spin-orbit effects in photodissociation of ionised rare gas trimers Indication of the charge localization: Stable configuration of the Rg 3 + on the ground electronic level. Vibrationally excited Rg 3 + cluster on the ground electronic level. Cluster is excited to a higher electronic level. Photon absorption Heating (Metropolis Monte Carlo) Dissociation (MD) Asymmetric decay Symmetric decay Channel 3 (three evaporated atoms) Channel 1 (one evaporated atom) Xenon SO constant = eV E( 2 P 1/2 ) – E( 2 P 3/2 ) = eV D 0 (Xe 3 + ) = eV Argon SO constant = eV E( 2 P 1/2 ) – E( 2 P 3/2 ) = eV D 0 (Ar 3 + ) = eV Krypton SO constant = eV E( 2 P 1/2 ) – E( 2 P 3/2 ) = eV D 0 (Kr 3 + ) = eV Experiment: Haberland, Hofmann, and Issendorff, J. Chem. Phys. 103, 3450 (1995).Next results: D. Hrivňák, R. Kalus, and F. X. Gadea, Europhys. Lett. 71 (1), pp (2005).