RESULTS I - Kinetic energy release

1. OSTRAVA Photodissociation of Rare-Gas Ionic TrimersDaniel Hrivňáka, René Kalusa, Florent X. GadéabaDepartment of Physics, University of Ostrava, Ostrava, Czech RepublicbLaboratoire de Physique Quantique, CNRS, Tolouse cedex, FranceFinancial support: the Grant Agency of the Czech Republic (grants No. 203/02/1204 and 203/04/2146),Ministry ofEducation of the Czech Republic (grant No. 1N04125). THEORY Hemiquantal dynamics with the whole DIM basis (HWD) M. Amarouche, F. X.Gadea, J. Durup, Chem. Phys. 130 (1989) 145-157 - meanfield molecular dynamics DIM Method Diatomic inputs Neutral diatoms - empirical data: Ar2 – R. A. Aziz, J. Chem. Phys. 99 (1993), 4518. Kr2 – A. K. Dham et al., Mol. Phys. 67 (1989) 1291. Xe2 – A. K. Dham et al., Chem. Phys. 142 (1990) 173.Singly charged diatoms: computed ab initio by I. Paidarová and F. X. Gadéa (1996, 2003, 2001) The spin-orbit constant used is of empirical origin. DIM extensions 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. F. O. Ellison, J. Am. Chem. Soc. 85 (1963), 3540. P. J. Kuntz & J. Valldorf, Z. Phys. D (1987), 8, 195. SIMULATION RESULTS I - Kinetic energy release Stable configuration of the Rg3+ on the ground electronic level. Ar3+ Xe3+ Heating(Metropolis Monte Carlo) Vibrationally excited Rg3+ cluster on the ground electronic level. Fig. 3 Xe3+ photodissociation. Kinetic energy distribution of charged (a, b, c) and neutral (d, e, f)fragments for photon energies 1.6 eV, 3.0 eV and 3.7 eV and three temperatures (150 K - solid line, 250 K - dashed line, 350 K - dotted line). Model DIM+SO. A general fragmentation pattern from experiment1 is confirmed by our theoretical calculations at low temperatures. Initial configuration is nearly linear and symmetric. After vertical ionisation the middle atom obtains only a small velocity, two remaining outer atoms gain high velocities of 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. The spin-orbit splitting of the Rg+ ion to the two states 2P1/2 and 2P3/2 plays an essential role in the theoretical and experimental results. Fig.1 Ar3+ photodissociation. Kinetic energy distribution of charged (a, b, c, d) and neutral (e, f, g, h)fragments forphoton energies 2.4 eV and 4.6 eV and three temperatures (50 K - solid line, 150 K - dashed line, 300 K - dotted line). hn Photon absorption (standard formula) The same configuration asprevious one. Cluster is excited to ahigher electronic level. Kr3+ Dissociation(molecular dynamics) Symmetric decay Asymmetric decay Cluster decays to single fragments following two main channels. Fig.2 Kr3+ photodissociation. Kinetic energy distribution of charged (a, b, c) and neutral (d, e, f) fragments for photon energies 2.1 eV, 2.8 eV and 4.4 eV and three temperatures (100 K - solid line, 200 K - dashed line, 300 K - dotted line). Model DIM+SO. 1Experiment: Haberland, Hofmann, and Issendorff, J. Chem. Phys. 103, 3450 (1995). Indication of the charge localization: RESULTS III Dissociation channels RESULTS II - Fragmentation time Ar3+ Fig. 4 Fragmentation time distribution for Ar3+. Temperature 150 K, model DIM (squares) and DIM+SO (circles). Fig. 7 Dependence on photon energy of the relative counts for main dissociation channels of Xe3+. Temperature 250 K, squares – channel “monomer + dimer”, circles – channel “three monomers”. Fig. 6 Dependence of the average fragmentation time on the photon energy for Ar3+ (150K), Kr3+(200K) and Xe3+(250K), model DIM (squares) and DIM+SO (circles). Average fragmentation time decreases with photon energy, but there is an up-jump for a photon energy about 2.5 eV for Kr and particularly Xe (see Fig. 6b, c). This jump is caused by pumping of kinetic energy to the potential energy of the charged fragment (transition between 2P3/2 and 2P1/2 state). Amplitude of the jump is proportional to the size of spin-orbit constant of the rare gas used (Ar – 0.117 eV, Kr – 0.444 eV, Xe – 0.874 eV). A dissociation to three monomers has been discovered at the given temperature and photon energy region with one exception you can see in Fig. 7b. Relevant decay to the dimer and monomer is observed only for Xe3+, model DIM+SO, photon energies between 2.3 and 3.0 eV. It is due to lack of kinetic (vibrational) energy, which is pumped to 2P1/2 state of the evaporated charged monomer. Fig. 5 Fragmentation time distribution for Xe3+. Temperature 250 K, model DIM (squares) and DIM+SO (circles). CESTC 2006, Zakopane, Poland, 24-27 September, 2006