J. J. Leventhal

Energy transfer in atom–diatom collisions: Vibronic excitation

Product state distributions from charge‐transfer collisions between Ar+–N2 and H+–O2 as well as collision‐induced excitation involving N+2 on He, Ar, and Xe are presented. These data, obtained from collision‐produced emission spectra, are compared with a Franck–Condon model for the excitation‐radiation process; significant deviations are observed and explained on the basis of a qualitative curve‐crossing model formulated to treat such vibronic excitation processes.

Dynamic model for vibronic excitation in low energy atom-molecule collisions☆

Abstract Product state distributions from low energy He + N 2 and N + 2 He collisions are presented. These data, obtained from collision-produced emission spectra, show severe deviations from Franck-Condon behavior which cannot be solely the result of molecular distortion arising from electrodynamic effects. A model based on consideration of the short-range interaction between the collision partners is proposed.

Energetics of HeH+ Formed in H2+–He Collisions

Kinetic‐energy distributions of forward‐scattered HeH+ ions resulting from H2+–He collisions have been experimentally determined for H2+ laboratory kinetic energies in the range 1.7–12.5 eV. These distributions have two main peaks over most of this primary ion energy range. The lower‐energy peak which appears to correspond to completely inelastic collisions is believed to result from enhanced collection efficiency, a conclusion which is supported by energetic considerations. The behavior of the higher‐energy peak, which corresponds to ions formed in the forward direction (center of mass), is consistent with theoretical calculations for the HeH+ species.

Two‐Channel Model for Electron Transfer in Ion–Molecule Collisions

A phenomenological model based on competition between charge‐transfer and atomic‐rearrangement (chemical reaction) channels is used to calculate the charge exchange cross section for Ar+–H2 collisions below 1000 eV. The energy dependence of the calculated cross section is in good agreement with recent data.

Measurement of atomic densities using radiation trapping

The apparent lifetimes of the 2P1/2 and 2P3/2 states of Na have been measured as functions of n, the atomic density, and the results compared to theory. It is shown that these measurements made under equilibrium, steady‐state conditions may be used to determine n under nonequilibrium, nonsteady‐state conditions. This technique of measuring n has advantages over the surface ionization technique, especially for values of n greater than about 1010 cm−3. Extension of the technique to other atoms and molecules is discussed.

Collision Mechanism Leading to the Formation of NO+ in O+–N2 Collisions

The energetics of the reaction O++N2→NO++N have been investigated in the laboratory for the kinetic‐energy range 3–12 eV. The results indicate that the product NO+ ion is formed with excess internal energy. The heats of reaction obtained are consistent with formation of NO+ in a stripping‐type collision process above about 4‐eV incident ion energy.

Electronic energy transfer in near‐resonant electron capture collisions of H+2 with metal atoms: Radiative and nonradiative transitions

Modes of energy disposal in electron capture of H+2 with metal atoms (Cs, K, Mg, and Zn) for ion velocities in the range 3–7×107 cm/s are examined using combined optical and beam scattering techniques. Radiative and nonradiative transitions are observed for processes occurring under near resonant conditions. The following branching sequences are identified: Branching ratios are dependent on the vibrational state and the nuclear separation (Franck–Condon factors) of the H+2 ion at the time of electron capture. The branching ratio decreases for the (triplet)/(singlet) formation for H2 produced from reactions of vibrationally relaxed H+2 ion with K or Cs. Under conditions of H+2 ion relaxation, the kinetic energy of scattered atomic hydrogen following radiative decay from 3Σ+g state of H2 increases, implying a shift in the 3Σ+g→3Σ+u continuum toward longer wavelengths. The results also show that, at these velocities, the reations occur under near‐resonant conditions with vertical transitions.

Luminescence from He+O2 collisions at low energy☆

The emission spectrum resulting from He+O2 collisions in the kinetic energy range 25–400 eV has been measured between 1940 and 8500 A. The results show that highly endoergic charge transfer processes dominate the spectrum, although exoergic processes with excited O2+ production also occur. The nearly resonant charge exchange process yielding ground state He atoms and O2+[c 4Σu−(v=0)] does not occur with high probability.

Production of excited OD+ in O+−D2 collisions at low relative energies (below 4 eV)

The energetics of OD+ ions formed in collisions of ground state O+ with room temperature D2 molecules have been studied at relative energies in the range 0.76–3.58 eV using ion beam techniques. Excited electronic states of OD+ are inaccessible below about 1.3 eV, so that product internal energy must be vibrational‐rotational excitation of ground state (X 3Σ)OD+ below this energy. It was found that OD+ is formed with internal energy over the entire energy range. The spectator stripping mechanism seems to predominate over the entire energy range.

Product state distributions from CO2+ −H2 electron transfer

Abstract Emission from excited CO + ions resulting from CO 2+ −H 2 charge transfer collsions have been analyzed to yield vibrational state distributions of these products. These state distribution and the observed spectra have been compared to model spectra calculated from known CO and CO + potential energy curves and a recently proposed semi-empirical curve for CO 2+ . The model calculations which depend on this CO 2+ curve do not adequately reproduce the data.