R. Candori

The N2Ar potential energy surface

Abstract The potential energy surface for the N 2 Ar system has been obtained assuming a spherical average interaction previously reported from this laboratory. The angular dependence has been assessed by a combined analysis of the integral and differential scattering cross sections and sonic spectroscope data. The potential energy surface is given via a parametric model. A similar potential energy surface for O 2 Ar has been obtained with the same procedure. This surface is an improvement of an earlier one, because it reproduces the differential total cross sections recently measured.

Scattering of magnetically analyzed F (2P) atoms and their interactions with He, Ne, H2 and CH4

Abstract An improved source of a beam of fluorine atoms has been characterized by magnetic analysis of sublevels for F( 2 P). Ground state and lower lying excited state potential energy curves for the interaction of fluorine atoms with He, Ne, H 2 and CH 4 have been obtained from measurements of integral scattering cross sections at thermal energies. The results for the rare gas systems are discussed in connection with previous work on Ar, Kr, and Xe fluorides; those for the H 2 and CH 4 systems provide information of fine structure effects on the long range pan of entrance channels for reactive potential energy surfaces.

Molecular beam studies of weak interactions for open‐shell systems: The ground and lowest excited states of rare gas oxides

Integral cross sections as a function of velocity for scattering of ground state oxygen atoms by the rare gases have been measured at thermal energy. Analysis of atomic sublevels by a Stern–Gerlach magnet allows a control of the relative contribution from different fine structure scattering channels. The results are analyzed using an adiabatic decoupling scheme to derive the interaction as a spherical part and an anisotropic component, from which information is obtained on the six lowest states of the rare gas oxides and on nonadiabatic coupling terms.

Multiproperty study of the HeN2 potential energy surface

Abstract The full anisotropic HeN 2 interaction is studied in detail by analysing several recent experimental data. The various theoretical potential energy surfaces which had been previously proposed are assessed by comparing their success in predicting results from scattering measurements and gaseous properties. A new empirical potential energy surface obtained by us via a simultaneous fitting of several experimental data is also proposed and tested. This last potential turns out to be the only one which correctly accounts for rotationally inelastic collisional behaviour, which reproduces within the experimental uncertainty second virial coefficients, integral and total differential cross sections and the diffusion and viscosity coefficients of HeN 2 mixtures. Its validity and reliability is therefore discussed in comparison with previous attempts at obtaining the full HeN 2 interaction and the bounds in the values of the parameters in the final form suggested for the present surface are analyzed in some detail via a vis the accuracy of the experimental data employed in the fitting procedure.

On the interaction potentials for the electronic energy transfer reactions Xe(3P0,2)+N2(X)→Xe(1S0)+N2(B 3Πg)

Abstract An analytical description of the interaction potentials of the title reactions is given. Based on an earlier, essentially repulsive model, it incorporates (a) for both entrance channels, ion-induced dipole contributions; (b) for Xe( 3 P 2 ), the splitting into three branches corresponding to the different electronic angular momentum projections; (c) for the exit channels, slight modifications of the van der Waals potential wells. The calculated characteristics of the entrance/exit potential crossings of this improved model explain qualitatively all important details of the observed product vibrational/rotational/fine structure distributions, including the exothermic channels not amenable to the previous description.

Structure and charge transfer dynamics of the (Ar–N2)+ molecular cluster

In this paper we have investigated the interaction potential and the charge transfer processes at low collision energies in the (Ar–N2)+ system. The angular dependence of the lowest doublet potential energy surfaces (PES), correlating with Ar+(2Pj)–N2 and Ar–N2+(2Σ,2Π), has been given in terms of spherical harmonics, while the dependence on the intermolecular distance has been represented by proper radial coefficients. Such coefficients, which account for van der Waals, induction, charge transfer, and electrostatic contributions, have been predicted by empirical correlation formulas. The PES so obtained have been employed to calculate cross sections for the charge transfer process Ar++N2→Ar+N2+ at low collision energy (E⩽2 eV). A good agreement between calculated and experimental cross sections is obtained by assuming that the duration of the nonadiabatic transition has to match the time required for the molecular rearrangement into the final vibrational state. As a consequence the efficient formation of ...

Accurate Ne-heavier rare gas interatomic potentials

Accurate interatomic potential curves for Ne-heavier rare gas systems are obtained by a multiproperty analysis. The curves are given via a parametric function which consists of a modified Dunham expansion connected at long range with the van der Waals expansion. The experimental properties considered in the analysis are the differential scattering cross sections at two different collision energies, the integral cross sections in the glory energy range and the second virial coefficients. The transport properties are considered indirectly by using the potential energy values recently obtained by inversion of the transport coefficients.

The neon-argon interatomic potential

Due to some new recent and accurate experimental results the Ne–Ar interatomic potential has been reexamined. The two multiproperty potentials available in the literature have been tested in their ability to reproduce all the experimental data available today . A new potential has been determined which allows a very good description of all the available experimental results, i.e., transport properties, second virial coefficients, and differential and integral cross sections in the thermal energy range; the new potential does not exhibit the inadequacies of the earlier multiproperty potentials.

Chemiluminescent reactions of excited calcium atoms with HCl and HBr: Selective charge-transfer “harpooning” and synchronized intermediate complex rearrangement

A “harpooning” mechanism is investigated for the chemiluminescent reactions of Ca*(1D2) atoms with HCl (leading to CaCl* in the A state) and with HBr (leading to CaBr* in both the A and B states). A model of the interactions in the entrance channels, which involves an electron jump and leads to a charge-transfer intermediate complex, accounts for the selective dependence of reactivity on the relative orientation between the molecule and the outer electronic orbital of the atom. The dynamical treatment incorporates in the Landau–Zener approach the synchronization between times for nonadiabatic transitions and for triggering the rearrangement of the intermediate collision complex. The treatment accounts for the observed features of the translational energy dependence of the cross sections: The steep initial increase with a pronounced maximum, the sharp decline and also fine details, such as a stairlike behavior.

On the dynamics of the vibrationally selective electronic energy transfer from metastable xenon atoms to nitrogen molecules

Abstract The energy transfer reaction Xe( 3 P 0,2 ) + N 2 (X) → Xe( 1 S 0 ) + N 2 (B 3 Π g ) is analyzed by extensive numerical calculations of the dynamics. The potential energy surfaces used were previously shown to account qualitatively for the experimental findings. The present calculations are aimed at an explanation of the branching ratios between the vibrational levels of the N 2 (B) product as previously measured at several collision energies. The collisions are treated as sudden with respect to molecular rotation and the reaction is assumed to be adiabatic on vibronic states. Those crossings between entrance and exit channels which are responsible for the nonadiabatic transitions are identified by symmetry analysis and numerical experiments, using the Landau-Zener theory. Information on the strength and radial dependence of the relevant coupling matrix element is obtained. The separability between vibrational and electronic degrees of freedom is discussed. In certain cases the nonadiabatic transitions are so fast that molecular rearrangement can be neglected (sudden behaviour), while in other cases they are slower than vibrations (adiabatic behaviour). In the sudden limit the Franck-Condon factors between the N 2 (X) and N 2 (B) vibrational wavefunctions have to be taken into account, but in the adiabatic limit they are unimportant.