A quadrupole mass spectrometric analyser for use in flame ionization is described, together with its application to the ions produced by traces of sodium, added as chloride, in premixed hydrogen-air flames. Negative ions (Cl¯ and OH¯) appear to be of subsidiary importance in the main ionization processes, which rather proceed through direct production of electrons. Nevertheless, it is established that the appearance of Cl¯ ions is consistent with dissociative attachment HCl+
e
¯ → Cl¯+H, rather than by three-body attachment Cl+
e
¯+
M
→ Cl¯+
M
. Hydroxyl ions probably are formed in the same way. The ratios of the amounts of
A
+
(alkali) and
A
+
. H
2
O (alkali monohydrate) ions have been measured in the cases of lithium, sodium and potassium. Equilibrium constants for the reaction
A
+
.H
2
O ⇌
A
+
+ H
2
O are obtained and heats of monohydration of 44, 28 and 17 kcal/mole deduced respectively for
A
≡ Li, Na, K. Small amounts of H
3
O
+
appear in the reaction zone because of traces of hydrocarbon impurities in the flame gas supplies. These are severely reduced by alkali addition, apparently by an exchange reaction
A
+H
3
O
+
→
A
+
+H
2
O+H, with a rate constant of 1.1 x 10
-8
cm
3
/s at 2000 °K, rather than by recombination with electrons produced by direct ionization of alkali H
3
O
+
+
e
-
→ H
2
O+H. In contrast with the steady production of
A
+
ions in the burnt gases by reactions of the type
A
+
M
→
A
+
+
e
¯+
M
, there is an anomalously high rate of production in the reaction zone. This appears difficult to explain without introduction of processes involving ‘hot’ electrons.
Binary-Encounter Model for Direct Ionization of Molecules by Positron-Impact
