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 H 2 + on Ar and Kr were measured at various energies between 5 eV and 40 eV. Several rainbows could be resolved for the systems H + -N 2 , H + -CO, H + -CO 2 and H + -SF 6 . In the case of H + -H 2 , secondary rainbows could be traced at higher energies (30 eV). Only the primary rainbow was observed for H + -CH 4 . The H 2 + -Ar and H 2 + -Kr systems also yielded rainbow structures. Broad additional maxima appeared at large angles for H 2 + -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 + -N 2 , CO, CO 2 , SF 6 and H 2 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 N 2 -H + ; 4.70 eV for CO-H + ; 5.10 eV for CO 2 -H + ; 3.66 eV for SF 6 -H + ; 4.04 eV for H 2 -H + . These values are averages because of the anisotropy of the potentials. The potential depth for the H + -H 2 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 H 4 -CH 4 were evaluated classically, ε (H + -CH 4 ) 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-H 2 + ) and ε (KrH 2 + ) 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 + ) + H 2 → ArH + (KrH + ) + H including the ArH 2 + and KrH 2 + intermediate states. They show that most of the reaction energy becomes free in the approach of the reactants Ar + +H 2 . This effect is less pronounced for the Kr + ( 2 P 1/2 )+H 2 -reaction and even a small threshold energy exists for the Kr + ( 2 P 3/2 )+H 2 -reaction. reaction