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Absolute doubly differential cross sections for ejection of electrons in three- and five-body collisions of 20 to 114-keV protons on atomic and molecular hydrogen
Abstract
A crossed-beam experiment was performed to detect ejected electrons from ground-state atomic and molecular hydrogen after collisions with 20- to 114-keV protons. Because a pure atomic hydrogen target is not readily attainable, a method has been devised which yields atomic to molecular hydrogen doubly differential cross section (DDCS) ratios. Since the molecular hydrogen DDCS's were independently measured, the atomic cross sections could be directly calculated. Absolute cross sections differential in electron energy and angle were measured for electron energies ranging from 1.5 to 400 eV and scattering angles from 15$\sp\circ$ to 165$\sp\circ$ with respect to the fast beam. Electrons and ions were energy analyzed by an electrostatic hemispherical analyzer, which has an energy resolution of 5% and is rotatable in the scattering plane about the collision center. Atomic hydrogen is produced by a radio-frequency discharge of the type devised by J. Slevin. Hydrogen gas effuses from a 1 mm diameter nozzle in a nearly cos $\theta$ distribution. The projectile beam intersects the thermal gas targets 4 mm below the tip of the nozzle. Dissociation fractions of 74% and atomic hydrogen densities of 7 $\times$ 10$\sp{11}$ cm$\sp{-3}$ were typical. The fraction of dissociated hydrogen was measured by detecting the reduced 9-eV ion signal from the molecular target when the RF is on. This characteristic ion signal originates from the coulomb breakup of the molecule and dissociative channels of excited H$\sbsp{2}{+}$. An auxiliary experiment was performed to determine the target densities with the aid of a low-resolution magnetic mass spectrometer after the slow recoil ions were extracted from the collision volume by a weak electric field. Comparisons of the atomic cross sections are made with theories such as the classical-trajectory Monte Carlo (CTMC) method, the plane-wave Born approximation (PWBA) and the continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximation.
Subject Area
Atoms & subatomic particles|Molecules
Recommended Citation
Kerby, George W., "Absolute doubly differential cross sections for ejection of electrons in three- and five-body collisions of 20 to 114-keV protons on atomic and molecular hydrogen" (1994). ETD collection for University of Nebraska-Lincoln. AAI9519537.
https://digitalcommons.unl.edu/dissertations/AAI9519537