E. A. Gislason

Dynamics of the Reaction of N2+ with H2, D2, and HD

Product‐velocity‐vector distributions have been determined for the reactive and inelastic scattering of N2+ by H2, D2, and HD. These distributions show that the reaction proceeds by a direct short‐lived interaction rather than by a long‐lived collision complex. Most products are scattered in the original direction of the N2+ projectile at a speed somewhat greater than calculated from the ideal stripping model. The internal excitation of N2D+ and N2H+ is very high and decreases somewhat with increasing scattering angle. For HD there is an isotope effect that favors N2H+ by large factors at small scattering angles, and N2D+ by smaller factors at large angles. The N2+ scattered from D2 shows very little elastic component, but does reveal an inelastic process which is probably the collisional dissociation of D2.

Collisional Excitation of Small Molecular Ions

We have determined velocity vector distributions for NO+ and O2+ scattered from helium. As expected, the small angle scattering is elastic, but at angles greater than 60°, inelasticity which increases with the scattering angle is apparent. For angles greater than 100°, this inelasticity represents vibrational excitation of the molecule–ion. For initial relative kinetic energies between 4.3 and 25 eV and 180° scattering, the variation of the inelasticity is consistent with a new, corrected version of the classical theory of vibrational excitation. Three methods of calculating the angular variation of the inelasticity are presented and found to be consistent with the experimental data.

Dynamics of the reaction of N+ with H2. III

We report measurements of the velocity vector distributions of the ionic products of collisions of Ar+ with D2 and He for relative energies between 2.26 and 9.1 eV. The ion ArD+ is produced by a direct interaction mechanism which gives considerable forward scattering. The nonreactive scattering of Ar+ by D2 is intense, nearly elastic, and very similar to the scattering of Ar+ by He. Differential reactive cross sections are determined, partially deconvoluted, and compared with results from several other laboratories.

Collision Induced Dissociation of Molecular Ions

Velocity vector distributions of the fragment ion products of the dissociative collisions of O2+, N2+, NO+, and N2O+ with He have been determined, using projectile‐target relative kinetic energies which are one to three times the bond energy of the molecular ion. The most probable dissociation event produces a fragment ion whose velocity is very nearly the same as that of the original projectile ion. Fragment ions also appear at smaller velocities and larger scattering angles, and the importance of these features increase with increasing initial relative energy. Three models for the dissociation are discussed, and it is concluded that a version of the stripping model is most nearly consistent with the data.

Dynamics of the Reactions of N2+ with CH4 and CD4

Product velocity vector distributions have been determined for the reactive and nonreactive scattering of N2+ by CH4, CD4, and Ne. In the most probable reactive events, N2H+ and N2D+ are scattered forward at almost exactly the velocity calculated from the ideal stripping model. At the higher projectile energies, the internal excitation of CH3 even for zero angle scattering is significant, and product internal excitation increases with increasing angle. A large isotope effect favoring abstraction of H over D was found. The nonreactive scattering showed the occurrence of highly inelastic collisions, even for small angle scattering, and a feature which may be due to the collisional electronic excitation of CH4 or of N2+ was discovered.

Product energy and angular distributions from the reaction of N+2 with isotopic hydrogen molecules

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Approximate Differential Cross Sections at Large Scattering Angles for Simple Repulsive Potentials

The classical deflection angle θ and the classical differential cross section I(θ) are examined in the region near θ=180° for three simple repulsive potentials: the repulsive power potential; the exponential repulsive potential; and the screened Coulomb potential. An expansion for θ valid at small impact parameters is carried through second order and compared with exact calculations of θ and I(θ). In most cases, the expansion is quite accurate in the region from θ=180° to θ=80°. Numerical formulas are given for evaluating the first two coefficients in the expansion. Interpretation of experimental cross sections using these results is discussed.