The effects of spin-exchange collisions between thermal electrons and optically oriented metastable helium ( ${2}^{3}{S}_{1}$ ) atoms have been observed in a flowing helium afterglow, and the exchange cross section has been measured. The source of electrons derives from Penning collisions between the 19.8-eV metastable atoms and impurity atoms which are titrated into the flow region. The presence of thermal electrons shortens the metastable-spin-state lifetime and reduces the magnitude of the optical-pumping resonance signal. The electron density is determined from the reduction of the metastable density. The exchange cross section is found to be 1.6\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$ .The effects of spin-exchange collisions between thermal electrons and optically oriented metastable helium (${2}^{3}{S}_{1}$) atoms have been observed in a flowing helium afterglow, and the exchange cross section has been measured. The source of electrons derives from Penning collisions between the 19.8-eV metastable atoms and impurity atoms which are titrated into the flow region. The presence of thermal electrons shortens the metastable-spin-state lifetime and reduces the magnitude of the optical-pumping resonance signal. The electron density is determined from the reduction of the metastable density. The exchange cross section is found to be 1.6\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$.

Physical ReviewJul 5, 196811 citations

ELECTRON COLLISIONS WITH TRAPPED, METASTABLE HELIUM

L. J. Uhlmann, R. G. Dall, K. G. H. Baldwin +1 more

International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC)Nov 1, 20060 citations

A crossed-beam time-of-flight study of metastable helium in collisions with helium, neon and argon

K B Fiering, S. R. Ryan, William H. Wing

Absolute velocity-resolved total integral cross sections have been measured for collisions of helium singlet (2 1 S 0 ) and triplet (2 3 S 1 2) metastable (He*) atoms with ground-state helium, neon, and argon atoms in the thermal velocity range of 1.0-3.5*10 5 cm s -1 . Additional measurements on the He*-Ne system with a large input aperture at the detector to suppress the sensitivity of the apparatus to elastic scattering failed to show the previously predicted (Arathoon) sharply rising velocity structure in the inelastic excitation transfer cross sections.Absolute velocity-resolved total integral cross sections have been measured for collisions of helium singlet (2 1 S 0 ) and triplet (2 3 S 1 2) metastable (He*) atoms with ground-state helium, neon, and argon atoms in the thermal velocity range of 1.0-3.5*10 5 cm s -1 . Additional measurements on the He*-Ne system with a large input aperture at the detector to suppress the sensitivity of the apparatus to elastic scattering failed to show the previously predicted (Arathoon) sharply rising velocity structure in the inelastic excitation transfer cross sections.

Journal of Physics B Atomic and Molecular PhysicsNov 14, 19823 citations

Metastability-exchange and depolarising collisions in xenon and krypton

V. Lefèvre-Seguin, Michèle Leduc

Collisions between rare-gas atoms in the 3 P 2 metastable state and in the ground state were studied. The metastable atoms were created by a discharge and oriented by optical pumping, and pressure broadening of their magnetic-resonance curves was measured. For xenon, mixtures of even and odd isotopes were used, leading to a determination of the cross section for metastability-exchange collisions. For krypton the results are reported for the disorientation of the metastable state in the natural gas. In addition the disorientation cross section has been measured of the krypton metastable state through collisions with helium.Collisions between rare-gas atoms in the 3 P 2 metastable state and in the ground state were studied. The metastable atoms were created by a discharge and oriented by optical pumping, and pressure broadening of their magnetic-resonance curves was measured. For xenon, mixtures of even and odd isotopes were used, leading to a determination of the cross section for metastability-exchange collisions. For krypton the results are reported for the disorientation of the metastable state in the natural gas. In addition the disorientation cross section has been measured of the krypton metastable state through collisions with helium.

Journal of Physics B Atomic and Molecular PhysicsAug 1, 197713 citations

Novel Experimental Approaches to Studies of Electron Metastable Atom Collisions

Mark E. Lagus

Jan 1, 19950 citations

The effects of spin-exchange collisions between thermal electrons and optically oriented metastable helium (

{2}^{3}{S}_{1}

) atoms have been observed in a flowing helium afterglow, and the exchange cross section has been measured. The source of electrons derives from Penning collisions between the 19.8-eV metastable atoms and impurity atoms which are titrated into the flow region. The presence of thermal electrons shortens the metastable-spin-state lifetime and reduces the magnitude of the optical-pumping resonance signal. The electron density is determined from the reduction of the metastable density. The exchange cross section is found to be 1.6\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$

{\mathrm{cm}}^{2}