F. Rebentrost

Diatomic interhalogen laser molecules: Fluorescence spectroscopy and reaction kinetics

Mixtures of halogen‐containing molecules and rare gases have been excited by a short pulse of high energy electrons. The D′→A′ transitions occurring between an ionically bound upper level and a weakly bound covalent lower level in the diatomic halogens F2, Cl2, and interhalogen compounds ClF, ICl, IF, IBr, BrCl, and BrF formed under these conditions have been studied systematically. Emission wavelengths calculated from a simple model are in good agreement with the experimental data. The processes responsible for the population of the upper level have also been studied. The exchange reaction of an electronically excited atom with a halogen donor molecule appears to be the key step in the kinetic excitation sequence. A rate equation model satisfactorily describes the time development of the observed halogen fluorescence. Based on these results, successful laser experiments have been conducted on several of the interhalogen systems.

On the effects of adsorbate aggregation on the kinetics of surface reactions

The effects of lateral interactions between chemisorbed reactants on the mechanisms of surface reactions are studied by Monte Carlo simulations for a model system. The model describes a reaction between two adsorbates, A and B, which upon reaction form a rapidly desorbing product. The surface is described by a square lattice with attractive nearest‐neighbor interactions between the A atoms; wAA/kT=−2.5. The B atoms are regarded as ‘‘random walkers,’’ unaffected by lateral interactions. (wAB=wBB=0.) The A atoms are allowed to aggregate before B is adsorbed on the surface. Reaction can occur when the much more mobile B’s reach the boundary of an ‘‘island’’ of A atoms. The island structures depend on the aggregation period allowed for A and on coverage. Most of the simulations model a reaction beginning after A aggregation has reached a long‐lived (yet nonequilibrium) state, characterized by finite and ramified islands with strongly indented boundaries. Typical island characteristics, such as their average b...

Semi-local pseudopotential calculations for the adiabatic potentials of alkali-neon systems

Abstract Pseudopotential calculations have been performed to obtain the adiabatic potentials fore the ground state and for several excited states of alkali-neon systems. Both the alkali ion-valence electron and Ne-valence electron interactions are represented by semi-local l-dependent pseudopotentials. Standard variational calculations were made in a basis set of Gaussian functions. The accuracy of the calculated potentials is assessed by comparison with the available experimental data and with results of other calculations. Overall agreement has been obtained. This indicates that a significant improvement in calculations of the adiabatic potentials of alkali-rare gas atoms can be achieved by applying an l -dependent pseudopotential technique.

On the fragmentation of benzene by multiphotoionization

The MPI fragmentation of benzene is analyzed on the basis of experimental data and the dissociation dynamics of C6H+6 at low excess energies. A multiple fragmentation mechanism with branchings is discussed in which vibrational energy is pumped into the C6H+6 ground state by photon absorption and subsequent radiationless transitions. Calculations are performed for a statistical, products phase space model and show remarkably good agreement with the experimentally observed fragment patterns vs laser intensity. About 60 eV/molecule are required to make C+ the most abundant ion, if all the energy were initially present in the C6H+6. By RRKM estimates of the C6H+6 decomposition rate it is concluded that such an assumption is not realistic and a model with multiple absorption and fragmentation steps applies.

Adiabatic potential curves for the Cd2 dimer

Abstract Potential energy curves and dipole transition moments for a number of electronic states of the Cd 2 dimer are presented and discussed. They are derived using the MRCI(SD) procedure for the valence electron of the species, while the core electrons are represented by semi-empirical l -dependent pseudopotentials. The effect of spin-orbit coupling is not investigated.

A statistical model for the fragmentation of benzene by multiphotoionization

Abstract A statistical products phase space model for the (multi) photon fragmentation/ionization of polyatomic molecules in strong laser fields is proposed and tested on benzene. The mechanism assumes multiple dissociations and branchings starting with energy rich benzene ions. Calculated and experimental fragment mass patterns versus laser fluence are shown to be in good agreement.

PSEUDOPOTENTIAL CALCULATIONS FOR THE POTENTIAL ENERGIES OF CA+-HE AND CA+-NE

Abstract The pseudopotential treatment used so far for neutral species is extended to the case of the singly charged calcium ion perturbed by helium and neon atoms. The calculations have been performed for the adiabatic potentials and dipole transition moments in dependence on internuclear separation. Spin-orbit coupling is considered in a semi-empirical manner following the ‘atoms-in-molecules’ model. The results are discussed in the context of recent experiments on trapping and laser cooling of Ca + ions in the presence of background gases.

CALCULATION OF GROUND- AND EXCITED-STATE POTENTIAL ENERGY CURVES FOR THE HG2 MOLECULE IN A PSEUDOPOTENTIAL APPROACH

Abstract Potential energy curves for electronic states of the Hg2 dimer are calculated using the SCF and MRCI scheme for the four valence electrons of the system, with the core electrons represented by ab initio quasirelativistic energy adjusted pseudopotentials. Computations are performed for the molecular states that dissociate to the Hg(1S)+Hg(1S, 3P, 1P, 7s3S, 7s1S, 7p3P, 7p1P) asymptotes. The calculated potential curves are split into spin-orbit components in a semiempirical manner following the “atoms-in-molecules” model. Comparison of the derived potentials with known experimental data shows overall good agreement between theory and experiment, although the theoretical potentials are somewhat too shallow.

Semi-local pseudopotential calculations for the potential energies of the CaHe and CaNe systems

Abstract Pseudopotential SCF/CI calculations in a GTO basis set have been performed to obtain the adiabatic potentials for the ground state and for several excited states of the CaHe and CaNe complexes. Semi-empirical l -dependent pseudopotentials are used to describe both the calcium ion-valence electron and rare gas atom-valence electron interaction. The e − -rare gas interaction en-compasses both the dipole and quadrupole terms. Spin-orbit interaction is not included in the calculations. Some direct and indirect relativistic effects on valence-electron orbitals are incorporated via the pseudopotentials. The potentials are presented both diagrammatically and in a tabulated form.

Potential energy curves for the Zn2 dimer

Abstract MRCI(SD) calculations have been performed for the adiabatic potential curves and dipole transition moments of diatomic zinc. Only the four valence electrons of the system are treated explicitly, whereas the atomic cores are replaced by the energy-adjusted pseudopotentials. The spin-orbit coupling has not been considered.