Spin-resolved Alignment and Orientation Effects in Atomic Collisions

Abstract

The density matrix parametrisation of collisionally excited atomic ensembles is generalised to account for projectile and target spin polarisations. The density matrix elements, containing spin-resolved alignment and orientation parameters, can be determined by measurements of the 'generalised Stokes parameters' introduced by Andersen and Bartschat (1994) to describe scattered-projectile-polarised-photon coincidence experiments. Focusing on electron impact excitation of light alkali-type targets and mercury, the present experimental status of such experiments is reviewed, in particular with regard to the 'perfect scattering experiment' whereby all independent scattering amplitudes are determined.

Electron spin-polarized alkaline-earth ions produced by multiphoton ionization

“…Electron spin-polarized ions can be used to probe various spin-dependent dynamics at a surface 9,10 and in gas phase collisions, which are of great importance in chemical physics. For the study of spin-dependence of atomic collisions, [11][12][13][14][15] spin-polarized alkali-metal atoms prepared by optical pumping have often been used as targets. The use of spin-polarized alkaline-earth ions instead of alkali-metal atoms would add another dimension to understanding spindependent collision dynamics.…”

Complete Determination of Excitation Amplitudes and Phases for the31DState of Helium

“…The table lists the Stokes parameters P i ͑i 1 4͒ and the scattering amplitudes a 0 , a 12 , and a 22 with the alternative phases representing the "real" and the "ghost" solutions, as determined from Eqs. (1) to (5). The equivalence of these solutions is illustrated by the derived atomic properties of the charge cloud, namely the linear polarization P lin , the alignment of the charge cloud g, the angular momentum L Ќ , and the height of the charge cloud ͑r`͒ [2], all identical for the alternative phases.…”

“…The orientation is defined as the nonisotropic population of the 1M and 2M magnetic substates and determines the angular momentum transferred during the excitation process. Work of this type has been reviewed [1,2] and forms part of the quest for quantum mechanically complete measurements [1][2][3][4][5] to determine the scattering amplitudes and relative phases for a unique state and specific scattering dynamics.Studies of the 2 1 P state characterization with the detection of two particles (the scattered electron and the single 2 1 P to 1 1 S photon) are extensive and essentially complete [2]. However, the complete characterization of the amplitudes and relative phases for higher angular momentum states requires a lowering of the scattering symmetry and hence the detection of an increasing number of photons.…”

“…The orientation is defined as the nonisotropic population of the 1M and 2M magnetic substates and determines the angular momentum transferred during the excitation process. Work of this type has been reviewed [1,2] and forms part of the quest for quantum mechanically complete measurements [1][2][3][4][5] to determine the scattering amplitudes and relative phases for a unique state and specific scattering dynamics.…”