Coherent excitation of cadmiumJ=0,1,2 autoionizing levels by electron impact

Abstract

We have measured (e, 2e) energy spectra in cadmium for the 4d Ss Sp J =1 autoionizing region.The ejected-electron energy range investigated was from 2.6 to 4.8 eV with an incident electron energy of 150 eV and a scattering angle of 3'. Small difterences were found in spectra taken at ejected-electron directions 180 apart. We ascribe these diA'erences to interference terms arising from coherent excitation of the J =1 and overlapping 5pnp J =0,2 autoionizing levels. A calculation of these eftects is presented that agrees quite well with the experimental data. We obtain experimental excitation amplitude ratios and assign a previously undetected autoionizing level to SPY D2.

Investigation of complex ionization amplitudes in cadmium by (e,2e) spectroscopy

“…(for reasons given below), we construct a model based on the plane-wave Born approximation (PWBA). Reference [5] The final continuum state~f ) may be represented as a coherent superposition of total angular momentum basis states~f ) = g cLszM~S sEl LSJM ), LSJM (2) X b js(8", E )PJs(cos8) (3) where P~s(cos8) is an associated Legendre polynomial for which the radical provides normalization.…”

“…We shall denote such pairs of spectra I+ and I,where the positive (negative) sign refers to the binary (recoil) side of the electron beam axis. When Il' && 1, the PWBA magnitudes [5,8] are proportional to E for J& 0, and are independent of E for J=O. The present experiments were carried out for K =0.2 a.u.…”

“…In previous exploratory work [5] we have shown how the presence of autoionization enables the isolation of interference effects between the dominant dipole and very weak nondipole processes in the electron-impact ionization of Cd. The experimental technique involves the measurement of coincidence spectra at ejected electron angles 180' apart; small differences in the spectra are due to the sum of interference terms formed from cross products of multipole amplitudes of different parity.…”

(e,2e) studies on cadmium autoionizing resonances

“…Below, we describe (e, 2e) experiments on Cd involving autoionizing levels, using techniques that we have previously developed. 4 The analysis of these experiments enables the extraction of the relative magnitudes and ratios of individual cross-terms.…”

Coherent excitation of autoionizing resonances by electron impact. Annual report, September 1991 - January 1993

“…Figure 1 shows binary and recoil spectra with the improved energy resolution (unpublished). Note the sharp feature at -4.2 eV in the recoil peak; in Ref (2) , Fig (4), this was imperfectly resolved and appeared as a shoulder on the main peak. At the time of writing, the PSD system has been installed and initial tests are being carried out.…”