Proton-impact excitation of HeI triplet levels

Angular momentum coherences of helium atoms excited by proton impact

“…According to this approach, excitation of helium atoms as well as of hydrogen atoms by 12.5 keV p-He collisions is essentially a quasimolecular process. The energy dependence of the excitation cross sections of the lsnd [13] and ls4f states [9] indicates that the quasimolecular excitation mechanism gradually looses its significance for p-He collisions when increasing the proton velocity to vp > 0.7 a.u. Further studies of angularmomentum coherences in the energy range above 12.5 keV should be helpful for finding the limits of validity of MO saddle dynamics.…”

“…Since the projectile is a bare nucleus, only He I singlet states are excited [9]. Therefore, when analyzing the spectrum of the impact radiation, one expects that only singlet lines appear.…”

“…Cross section measurements [9,13] have shown that the high-angular momentum states (lsnd and ls4f) of He I are strongly excited by 10-15 keV proton impact. We conclude from the present experiments that within each n-shell essentially only one pure 127 and one pure ~H He I state is formed by 12.5 keV p-He collisions.…”

Analysis of impact-excited HeI states by applying magnetic and electric depolarization techniques

“…Due to Wigner's spin conservation rule [16], excitation of triplet states involves an exchange of electrons between projectile and target. Therefore, the excited electron of the He target atom is likely to originate from the projectile.…”

“…The homogeneous magnetic and electric fields (z axis) were perpendicular to the projectile beam (x axis), and the intensity III (B~) of the impact radiation (emitted in y direction and linearly polarized in x direction) at 2(41D-21p)_ 492 nm and 2(3 1D-21p) = 668 nm was measured as a function of the magnetic field strength B~. The general outline of the experimental set-up has been described in [16]. H +, D] or He + ions were extracted axially from a Penning ion source [17], massseparated in a bending magnet and focussed on the target chamber.…”