Spin-Exchange-Induced Circularly Polarized Molecular Fluorescence

Electron Scattering by Atoms, Ions, and Molecules

“…In many cases, spin-effects are largely masked by the averaging over molecular orientations. However, Green et al (2004) recently found an example of circularly polarized molecular fluorescence induced (a) Angle-integrated Stokes parameter P 2 for polarized-electron-impact excitation of the (6s6p) 3 P 1 state of Hg as a function of the incident electron energy. The experimental data of Wolcke et al (1983) are compared with theoretical predictions from a Breit-Pauli R-matrix approach developed by Bartschat et al (1984).…”

Alignment and orientation of diatomic molecules induced by polarized electron impact

“…Our group has done a number of experiments with both H 2 and N 2 targets to try understand this atomic/molecular difference. In an initial report, we presented the first measurements of non-zero circular polarization for molecular fluorescence from H 2 due to spin exchange [5]. In this paper we report recent extensions of these results to include the linear polarization (Stokes parameter P 1 ) and data for D 2 .…”

Angular Momentum Partitioning in the Dissociation of Diatomic Molecules

“…This is because the spin-orbit coupling time is comparable to the internuclear rotational period, ~10 -13 s. Hydrogen, on the other hand, is a Hund's case b) molecule, meaning that the spin is much more loosely tied to the internuclear axis. While its rotational period is still ~10 -13 s, its spin-orbit coupling time is closer to ~10 -10 s. Thus hydrogen can retain a better "memory" of the initial spin direction [12]. We have investigated several other transitions in molecular hydrogen, and find them to be polarized as well, although with generally lower polarization than that shown in Figure 1.…”

“…Thus it should be possible to investigate angular momentum transfer to the molecular fragments by investigating the circular polarization of atomic fluorescence. Using this idea, our group and the Perth group [12,13]. These data are shown in Figure 2.…”

“…Thus, if we excited a pure molecular triplet state by exchange, T = 2/3 [1]. Following dissociation, we assume that the atomic 3s, 3p, and 3d states all have equal spin polarization T', and that this polarization is completely coupled to the orbital angular momentum in the case of the 3p and 3d states, while we ignore hyperfine depolarization [12]. Taking into account the branching ratio between Hα and Lyα radiation (see Figure 3), assuming that light from the 3s state is unpolarized, and using published data for the relative production cross sections for 3s, 3p, and 3d states as the result of electron impact dissociation of H 2 [14], we can infer a threshold value of T' =0.37.…”