Streuung von Ionen. III. Regenbogeneffekt bei der Streuung von H+ an N2 , CO, CO2 , SF6, H2 und CH4 sowie von H2 + an Ar und Kr

Abstract

Differential scattering cross sections of H⁺ on various molecules and of H₂ ⁺ on Ar and Kr were measured at various energies between 5 eV and 40 eV. Several rainbows could be resolved for the systems H⁺-N₂, H⁺-CO, H⁺-CO₂ and H⁺-SF₆ . In the case of H⁺-H₂ , secondary rainbows could be traced at higher energies (30 eV). Only the primary rainbow was observed for H⁺-CH₄ . The H₂ ⁺-Ar and H₂ ⁺-Kr systems also yielded rainbow structures. Broad additional maxima appeared at large angles for H₂ ⁺-Kr which were atttributed to the crossing of potential curves. The rapid oscillations could not be observed. The measured differential cross sections for the systems H⁺-N₂ , CO, CO₂, SF₆ and H₂ were fitted by a procedure described in part I using a simple Morse potential. The equilibrium distances r_m were estimated from the relation r_m = 0.7-r_g (r_g: gaskinetic radius of the molecule) which was found to hold approximately for the H⁺-noble gas systems. The following potential depths e were obtained: 4.15 eV for N₂-H⁺; 4.70 eV for CO-H⁺; 5.10 eV for CO₂-H⁺; 3.66 eV for SF₆-H⁺; 4.04 eV for H₂-H⁺. These values are averages because of the anisotropy of the potentials. The potential depth for the H⁺-H₂ system is little smaller than the theoretical value of 4.56 eV. This is attributed to nontriangular configurations in the scattering process. The scattering experiments with the system H⁴-CH₄ were evaluated classically, ε (H⁺-CH₄) was found to be 3.8 eV only. The large difference to the theoretical value ε = 5.45 eV is explained by the inadiabacity of the scattering process with respect to the movement of the H atoms in methane. ε (Ar-H₂ ⁺) and ε (KrH₂ ⁺) were found to be (1.3 ± 0.2 ) eV and (1.1 ± 0.2 ) eV, respectively. Energy level diagram are dicussed for the ion-molecule reactions Ar⁺ (Kr⁺) + H₂ → ArH⁺ (KrH⁺) + H including the ArH₂ ⁺ and KrH₂ ⁺ intermediate states. They show that most of the reaction energy becomes free in the approach of the reactants Ar⁺+H₂. This effect is less pronounced for the Kr⁺ (²P_1/2)+H₂-reaction and even a small threshold energy exists for the Kr⁺ (²P_3/2)+H₂-reaction. reaction