Elastic and Inelastic Scattering of Low-Velocity H— Ions in Hydrogen

Abstract

An improved apparatus for the production of beams of negative ions and the measurement of the elastic and inelastic scattering of negative ions in gases at low pressures in briefly described. The measured cross-sections are given for the scattering of 4—400 ev H— ions in hydrogen. In the range 4—40 ev (1.1—1.8 A) the interaction potential derived from the elastic scattering is V (ev) = —4.64×10—32/r4 (r in cm) which is close to the theoretical polarization interaction. The inelastic scattering is presumed to be due to electron detachment. The inelastic cross section increases from 1 cm—1 at 7 ev to 8.7 cm—1 at 395 ev. Above 75 ev the measured elastic cross section increases with increasing ion energy. This is attributed to the appearance of inelastic collisions which result in electronic excitation of the hydrogen molecules.

Potential energy and dipole moment surfaces of H3− molecule

“…While never observed in the ISM, the collisions between H 2 and H − , and of their isopotologues, have been studied in a number of laboratory experiments back to the 1950's [25][26][27][28][29][30][31].…”

“…[16]. It is worth to mention a stand alone study by Robicheaux [18] confirming the stability of H − 3 (and similar anions), where the PES was derived from the scattering length for the electron-H 2 collisions, and from the polarizability of H 2 .While never observed in the ISM, the collisions between H 2 and H − , and of their isopotologues, have been studied in a number of laboratory experiments back to the 1950's [25][26][27][28][29][30][31].Such collisions should also play a role in processes in tokamaks, especially if the negative…”

Dynamics of (H−,H2) collisions: A time-dependent quantum mechanical investigation on a new ab initio potential energy surface

“…The neutral counterpart H 3 and its isotopic analogs have been studied over the years. 7 Early measurements of the elastic and inelastic integral reaction cross sections for (H Ϫ ,H 2 ) collisions 8,9 were followed by Haq, Doverspike, and Champion 10 who measured the same for the reaction H Ϫ ϩD 2 . 6 In comparison, the (H Ϫ ,H 2 ) system has been studied much less.…”

Reactive Scattering for Different Isotopologues of the H3– System: Comparison of Different Potential Energy Surfaces

“…Reactions of hydrogen systems are of particular interest in this respect because they are amenable to the most rigorous theoretical treatment and thus represent ideal prototype cases for a detailed comparison of theory and experiment. The negative ion H 3 – has been investigated experimentally and theoretically over the past 50 years. − The potential energy surface (PES) of H 3 – is totally different from that of H 3 + , but it is very similar to that of H 3 , including the anisotropy, barrier height, and other characteristics. The charge-induced dipole interaction leads to a shallow well in the H 3 – molecule at greater H – ···H 2 distances; Stärck and Meyer found a well depth of 0.048 eV at R = 6.183 Bohr and r = 1.413 Bohr.…”