Abstract
Charge-exchange cross-sections for H
+
, D
+
, O
+
2
, H
+
2
, O
+
, CO
+
and N
+
2
in A; D
+
, O
+
and N
+
in Kr; D
+
, C
+
and Br
+
in Xe, and O
+
in H
2
O have been measured between 25 and 4000 eV energy by a method previously described. The normal atomic collision cross-sections rise to a maximum at a voltage which depends on the value of Δ
E
√
M
for the process,
M
being the atomic mass and Δ
E
the energy defect of the reaction. Collisions between negative ions and atoms have been studied with the same apparatus, the cross-section of the detachment reaction
X
-
+
Y
→
X
+
e
+
Y
— Δ
E
being obtained. For S
-
, Br
-
, I
-
, C
-
, P
-
, Li
-
in Ne, and H
-
in He, Ne, A, Kr, Xe, this rises with increasing energy of the incident ion. For O
-
in He, Ne, A, Kr, Xe, Cl
-
in He, Ne, A, Kr, Xe, and F
-
in Ne, Kr, Xe the cross-section at low energies is unexpectedly large for the value of Δ
E
√M. This may be interpreted as being due to the presence of excited states of these ions, of low electron affinities, in the beam. With O
-
, a low energy electron bombardment source gave smaller cross-sections, i.e. a smaller proportion of excited ions.
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