Investigation of spin-orbit effects in the excitation of noble gases by spin-polarized electrons

Abstract

We have measured the integrated Stokes parameters of the light emitted following the impact excitation by polarized electrons of the np 5 (n+1)p [5/2] We have measured the integrated Stokes parameters of the light emitted following the impact excitation by polarized electrons of the np5 ( n + l)p [5/213 states in Ne (n =2), Ar (n =3), Kr ( n =4), Xe (n = 5 ) , and the np5 (n + 1 )p [5/212 state in Kr. The near-threshold linear-polarization fractions 7, were consistent with zero for all of the J = 3 states measured, providing no evidence of Mott scattering. For J = 2 excitation, 7 , shows the clear influence of the intermediately coupled nature of the state. At threshold, the measured circular polarization 77, and linear polarization 7, for the J =3 states agree well with the LS-coupled threshold predictions. These results provide the basis for optical measurements of electron polarization.

Spin-Exchange-Induced Circularly Polarized Molecular Fluorescence

“…This is quite different from electron excitation of the alkali atoms, where P 3 falls to zero by 10 V above threshold [20]. However, a long tail is characteristic of the pure exchange excitation of noble gas atoms by polarized electrons [6]. Since the H 2 molecule is a closed-shell system, it seems reasonable that the excitation process would resemble the noble gases more than the alkalis, even if the molecule subsequently dissociates.…”

“…Within their statistical uncertainty of 2 10 ÿ3 the Münster group found P 3 to be nil. In contrast, experiments with noble gas targets, in which triplet states are produced by pure exchange excitation, result in large values of P 3 [6,8].…”

An inline optical electron polarimeter

“…8 These problems are solved by using helium as the target gas. 3 have shown that an optical electron polarimeter can also be based on any of the heavy noble gases.…”

“…This is not desirable as these higher states will not generally contain well-characterized information regarding the spin of the impact electron. 3,4 However, because of the energy dependance of the various excitation cross sections, the effect of cascades should not significantly effect the polarization measurements until the incident beam energy is greater than 22 eV.…”

“…An alternative polarimeter is based on the impact excitation of an atomic target and measuring the degree of circular polarization in the subsequent optical decay. [3][4][5] The incident electron polarization information is conveyed to the atom by exchange excitation from a singlet ground state to an excited triplet state. Since it is the orientation of the angular momentum of the atom that gives rise to circularly polarized fluorescence, one has to make a judicious choice of which angular momentum states to monitor in the optical decay process.…”