Atomic hydrogen revisited: electron impact excitation to H(2p) at 54 eV

Abstract

New measurements of the three reduced Stokes parameters for 54.4 eV electron impact excitation of the 2p state of atomic hydrogen support convergent close coupling and propagating exterior complex scaling theoretical values within two standard deviations and over a larger angular range of 2°–140° than earlier work. Whereas the present measurements and theoretical values of the circular polarization Stokes parameter P3 agree, they differ by up to about four standard deviations from the measurements by Gradziel and O'Neill (2004 J. Phys. B: At. Mol. Opt. Phys. 37 1893) in the vicinity of 30° electron scattering angle and so do not support their explanation of an increased significance of electron exchange for this excitation process at 54.4 eV. We explore some variations in experimental methods and their implications for the measurements.

A complete numerical approach to electron–hydrogen collisions

“…PECS reduced Stokes parametersP 1 ,P 2 andP 3 and related parameters P l , γ and P + for e-H 1s-2p scattering at E 0 = 54.4 eV. CCC box-based calculations (CCC-B) [40] and measurements of Yalim et al [65], Gradziel and O'Neill [64] and Williams and Mikosza [66] are also shown.…”

Electron Scattering by Atoms, Ions, and Molecules

“…Figure 8.19 shows the angle-integrated cross section for elastic scattering and electron-impact excitation from the (1s) 2 S state of atomic hydrogen. The excellent agreement between predictions from the CCC, RMPS, and IERM methods, as well as with the experimental data of Williams (1988), indicates that these sophisticated methods can indeed solve this problem to a very high degree of accuracy. Stepanovic et al (2006) recently measured the angle-integrated cross sections for electron-impact excitation of the 3 3 S and 3 1 S states of helium shown in figure 8.20.…”

“…The reduced Stokes parameters, P 1 , P 2 and P 3 for the H(2p) state at an incident electron energy of 54 eV. Closed squares, Yalim, Cvejanovic and Crowe (1997); closed and open circles, Williams and Mikosza (2006); closed triangles, Gradziel and O'Neill (2004); open triangles, O'Neill et al (1998);open squares, Nic Chormaic, Chwirot and Slevin (1993); open diamonds, Williams (1986); full line, the PECS theory of Bartlett et al (2005). Adapted from Williams and Mikosza (2006 More detailed reviews of angular and polarization correlation and superelastic scattering studies were given by Andersen, Gallagher and Hertel (1988) Andersen et al (1997), and Andersen and Bartschat (2001).…”

“…The RMPS (solid line), IERM (dashed line), and CCC (dash-dotted line) curves are barely distinguishable. The small dots represent the experimental data ofWilliams (1988). (FromBartschat et al (1996c).…”

Comparison of experiment and theory for superelastic electron-collision studies from laser-aligned magnesium

“…The electron-photon coincidence technique has been used to study collisions with different atomic targets, both experimentally and theoretically. These include the lighter targets hydrogen [4][5][6], helium [7,8], and magnesium [9,10]; intermediate targets including calcium [11][12][13][14][15][16], neon [17][18][19], and zinc [20][21][22][23]; and heavier targets including cadmium [24][25][26], lead [27], and mercury [28][29][30][31][32][33].…”