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RESULTS I: Comparison for the different rare-gases

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RESULTS I: Comparison for the different rare-gases

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  1. Photodissociation of Rare-Gas Trimer CationsDaniel Hrivňáka, René Kalusa, Florent X. GadéabaDepartment of Physics, University of Ostrava, Ostrava, Czech RepublicbThe Nanoscience Groupe, CEMES, CNRS, Tolouse, 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). OSTRAVA 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 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 Method 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: Comparison for the different rare-gases Stable configuration of the Rg3+ on the ground electronic level. A general fragmentation pattern from experiment1 is confirmed by our theoretical calculations at low temperatures2. 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. Heating(Metropolis Monte Carlo) Symmetric decay ratio Kinetic energy release Argon SO constant = 0.117 eV E(2P1/2) – E(2P3/2) = 0.175 eV D0(Ar3+) = 1.592 eV Vibrationally excited Rg3+ cluster on the ground electronic level. hn Photon absorption (standard formula) Krypton SO constant = 0.444 eV E(2P1/2) – E(2P3/2) = 0.666 eV D0(Kr3+) = 1.375 eV The same configuration asprevious one. Cluster is excited to ahigher electronic level. Xenon SO constant = 0.874 eV E(2P1/2) – E(2P3/2) = 1.311 eV D0(Xe3+) = 1.245 eV Dissociation(molecular dynamics) Symmetric decay Asymmetric decay Cluster decays to single fragments following two main channels. 1Experiment: Haberland, Hofmann, and Issendorff, J. Chem. Phys. 103, 3450 (1995). Indication of the charge localization: 2Vibrational temperature of the clusters before simulated photon absorptionis 150 K for the plots above. CONCLUSIONS RESULTS II: Temperature effects in Xe3+ cation • Generally, a very good agreement between experimental and computed data has been obtained. The HWD-dynamics, based on the DIM approach, is well suited for analysis of this problem. • Inclusion of the spin-orbit coupling to the computational model is necessary. • The general experimental fragmentation pattern has been confirmed by our calculations in the temperature range 150 K – 400 K. • The total kinetic energy of the photodissociation fragments increases linearly with energy of the photon, but there is a discrete down-jump for a sharply defined photon energy. This jump is clearly caused by pumping of the kinetic energy to the energy of the charged fragment (transition between 2P3/2 and 2P1/2 state). • The experimental curves of the symmetric decay ratio differ partially from our curves computed at low temperatures in the region of the higher photon energies. In the case of xenon, this difference vanishes for the simulation temperature about 300 K, but a good agreement in the intensity of the main peak is now disturbed. Plausible explanation of this problem will require further calculations. • Temperature induced structural changes are the most suspicious in the problem mentioned above. In the case of the xenon trimer, the phase changes to a liquid phase seems to occur at temperatures about 220 K. A charged dimer core with one neutral atom attached appears for the higher temperatures with the non-negligible probability. Kinetic energy release Structural changes(Monte Carlo simulation) Symmetric decay ratio 1Lindemancoefficient =(0: solid phase, 1: liquid phase). 2Core atoms = atoms with the non-negligible charge. Computational model: DIM+SO+ID-ID(dmp).ID-ID interaction is damped properly for short distances (I. Last, T. F. George, J. Chem. Phys. 93 (1990) 8925). 3Structural number = Q1 – Q2+ Q3(- Q4)(0: dimer or tetramer core, 0.5: trimer core).

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