Formation of negative ions by charge transfer: He/sup -/ to Cl/sup -/ Page: 4 of 13
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Schlachter et al. measured an optimum He* fraction of 1.4X
for 6-keV He* in cesium vapor. The Belfast group stud.>d
similar systems.1® Formation of He* by charge transfer has
been studied in metal-vapor targets other then cesium17;
results are shown in Fig. 2. A He* beam of 70mA at 10.5 keV
has been produced by charge transfer in sodium vapor.®
The He* ion 1s believed to have only one bound state, the
(ls2s2p)4Pj state (J = 5/2, 3/2, 1/2), with a binding energy
of 0.078 eV and a lifetime of about 500uS (J > 5/2). Some
experimenters have claimed the existence of a long-lived
(Is2p2)2p stat? of He*; recent calculations1® and
photodetachment2® studies do not support the existence of this
state. There is no bound state of He*, nor of the other rare
gases (except He).
M,' ENERGt 25 »«v
Fig. la Charge state fractions Fig. lb Confuted fractions of He
as a function of target atoms in singlet and
thickness for 25-keV He* metastable triplet
in cesium vapor.1® states for 25-keV He*
in cesium vapor.1®
The Li* ion is (ls22s2)1S and is bound by 0.62 eV.
Equilibrium yields have been reported by the Aarhus group® for
Na, K, and Cs vapor targets; conversion efficiencies at low
energies nave been reported by Steffens.21 Results are shown
in Fig. 3; the conversion efficiencies (1-20 keV) clearly He
below the equilibrium yields, as would be expected. The Na*
ion is (3s2)Is, with a binding energy of 0.55 eV. The only
results for formation by charge transfer are shown 1n Fig. 4
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Schlachter, A.S. Formation of negative ions by charge transfer: He/sup -/ to Cl/sup -/, article, December 1, 1983; [Berkeley,] California. (digital.library.unt.edu/ark:/67531/metadc1074466/m1/4/: accessed January 24, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.