Electric dipole moments of impact-excited He atoms

Angular momentum coherences of helium atoms excited by proton impact

“…They become evident if the impact-excited state of the helium atom is essentially formed during the final phase of the collision process where the axis of the collision system is already nearly parallel to the proton beam and, therefore, the evolution of the collision system is essentially independent of the impact parameter. We shall show below that the finalphase evolution is essentially a quasimolecular process as has been conjectured by van We pointed out earlier [2,8] that the collisional excitation of high-/He I states as welt as the formation of states with large electric dipole moments is strongly determined by inertial forces acting on the electron cloud when the quasimolecular system transforms into separated atoms. The final phase of a p-He collision with only one excited electron is a particularly simple one.…”

“…This technique could also be used for investigating angular momentum coherences of helium atoms [2,8] in spite of the rather large energy separations. In particular, the coherent excitation of the 1 s 4d and 1 s 4f configuration of He I by H+-ion [2] and He-atom impact [8] was analyzed where the energy separation would give rise to a beat frequency as high as (.O4d,4f~,~2" l011 Hz.…”

“…However, the collision time ~co11, i.e. the interval, where the interaction between the colliding particles affects the evolution of the collision system, may be longer, in particular, if Vp is small (Vp<Vs) [2]. Considering the excitation of neutral atoms by charged particles, for example protons, the collision process is finished only when the influence of the Coulomb field Fp of the receding charged projectile on the evolution of the impact excited state is negligible.…”

“…In particular, the coherent excitation of the 1 s 4d and 1 s 4f configuration of He I by H+-ion [2] and He-atom impact [8] was analyzed where the energy separation would give rise to a beat frequency as high as (.O4d,4f~,~2" l011 Hz.…”

Coherent excitation of H(n=2) in H+, H - He collisions

“…Similar asymmetries were observed by Krotkov and Stone for H(n=2) excitation in H-He, Ar collisions [18], and, quite recently, by Aynacioglu etal. for He(4d, 4f) and He(5f 5g) excitation by H~-impact [19]. A polarization study of these asymmetries was first performed by Haverier et al [2] for H(n=3) excitation in 40-80 keV H ÷ -He collisions.…”