Angle-energy distributions of Penning ions in crossed molecular beams. I. Evidence for discrete nonadiabaticity in the He*(2 sup 1 S )+H,D r arrow He+H sup + ,D sup + + e sup minus reaction

Journal Article · Fri Feb 15 04:00:00 EST 1991 · Journal of Chemical Physics; (USA)

DOI:https://doi.org/10.1063/1.459835· OSTI ID:5828989

Khan, A; Siddiqui, H R; Siska, P E ^[1]

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1. Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (US)

Relative doubly differential cross sections for the Penning ionization of H and D by He*(2 {sup 1}{ital S}) are reported at a mean collision energy of 9.2 kcal/mol for H and 7.9 for D in an experiment employing crossed supersonic beams and a rotatable mass spectrometer detector. The products are scattered sharply forward in the center-of-mass frame, with release of an additional 3.5 kcal/mol into translational energy at the peak of the recoil distribution. The energy release is significantly lower than predicted on the basis of quantum dynamics on a single adiabatic {ital ab} {ital initio} complex potential, or of the experimental low-energy Penning electron spectrum (PIES). Discrete nonadiabatic behavior is suggested and a model is developed based on modifications of {ital ab} {ital initio} potentials, Penning ionization atom--atom theory on a single complex potential, and an adiabatic-velocity modification of Landau--Zener curve-crossing theory (which may be more generally useful). The dynamical model compares well with exact two-state complex potential calculations for the magnitude and energy dependence of the total ionization cross section, and improves the emulation of both the low-energy PIES data and our recoil distributions. Significant modifications to the {ital ab} {ital initio} potentials include a deepening of the well in the He*(2 {sup 1}{ital S})+H adiabatic potential by 2.0 to 10.2{plus minus}1 kcal/mol, a quadrupling of the magnitude of the resonance width, and a reduction in the adiabatic splitting at the avoided crossing between 2 {sup 1}{ital S} and 2 {sup 3}{ital P} potentials. Our low-energy calculations suggest that available data on the associative ionization (HeH{sup +}) branching fraction is inconsistent with the PIES data.

• OSTI ID: 5828989
• Journal Information: Journal of Chemical Physics; (USA), Journal Name: Journal of Chemical Physics; (USA) Vol. 94:4; ISSN JCPSA; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ANGULAR DISTRIBUTION
ATOM COLLISIONS
ATOM-ATOM COLLISIONS
BEAMS
COLLISIONS
CROSS SECTIONS
DEUTERIUM
DIFFERENTIAL CROSS SECTIONS
DISTRIBUTION
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY SPECTRA
FLUIDS
GASES
HELIUM
HYDROGEN
HYDROGEN ISOTOPES
IONIZATION
ISOTOPES
LIGHT NUCLEI
MASS SPECTROSCOPY
MOLECULAR BEAMS
NONMETALS
NUCLEI
ODD-ODD NUCLEI
PENNING EFFECT
RARE GASES
SPECTRA
SPECTROSCOPY
STABLE ISOTOPES