Double excitations of helium

Journal Article · Wed May 01 04:00:00 EDT 1996 · Bulletin of the American Physical Society

OSTI ID:394176

Menzel, A

The double excitations of helium offers an ideal case for investigating electron dynamics in a three-body system. The author`s study of the He {sup 1}P{sup o} double excitations comprises measurements of the partial photoionization cross sections {sigma}{sub n}(He{sup +}) and the partial photoelectron angular distribution parameters {beta}{sub n} for the series N(K,T){sub i}{sup A} up to the N=5 threshold. The experiment was peformed at the ALS undulator beam line 9.0.1., which provided a photon flux of 2 x 10{sup 12} photons per second with a small photon energy bandpass of 7 to 12 meV. This level of differentiation, along with the small bandpass, offers the most critical assessment of the dynamics of the two-electron excitations to date. The principal series K = N {minus} 2 are clearly delineated in both {sigma}{sub n} and {beta}{sub n}. The {beta}{sub n} show all minor series with N = K {minus} 4 very clearly, in contrast to measurements of the total absorption cross section. Excellent accord between experiment and theory, particularly the hyperspherical close-coupling method, was found for the dynamic properties in all instances, including the interference pattern due to an overlap of N = 5 and N = 6 series members. Generally, the Rydberg series of resonance-induced profiles vary greatly depending on the final ionic state He{sup +}(n), whereas the peak-to-valley variation in the {sigma}{sub n} within a given series N is of similar magnitude for all n. Interestingly, a striking systematic trend is noted through the various series: the resonance-induced profiles for both the {sigma}{sub n} and {beta}{sub n} of the photoelectron satellites are virtually identical provided the final ionic state He{sup +}(n), n {ge} 2, is reached via an excited series N with {Delta} = 1, or {Delta} = 2, where {Delta} = N = n. This overall pattern might be attributed to the general similarity of states with the same set of approximately good quantum numbers (n {minus} K), A, and T.

• OSTI ID: 394176
• Report Number(s): CONF-9605105--; CNN: Grant PHy-9207634: Grant PHY-9507573
• Journal Information: Bulletin of the American Physical Society, Journal Name: Bulletin of the American Physical Society Journal Issue: 3 Vol. 41; ISSN BAPSA6; ISSN 0003-0503
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
EXCITED STATES
HELIUM
PHOTOIONIZATION
THREE-BODY PROBLEM