KOTES
1210
BF, and similar derivative^,^ now allow an experimental evaluation of the heat of formation of the BY2 radical. Consider the following reactions which might occur in the ionization chamber of a mass spectrograph to produce BF2+ e -I-BFdg) -c RFzYg) e BFdgi -., BF2+(g)
+
If reaction 1 holds
+ F ?+ F- 4-e
(1)
(2)
+ I(BF2) + AHfo(F) -AHto(BF3)
With the appearance potential of BF2+ selected as 16.5 f 0.3 e.v.,I2 the ionization potential of BF2 given as 9.4 f 0.1 e . ~ . AH? , ~ (F) = 0.8 e . ~ . ~ computes and AHfo(BF3) = -11.7 e . ~ . ,one AHfO(BF2) 6 -5.4 f 0.4 e.v. -124 f 9 kcal./ mole. If reaction 2 holds
AHfO(BF2) f I(BF9) +
AHfO(F-) - AHf'(BF3)
With AHfo(F-) = -2.8 e.v.6one computes AHrO(BF2)
< -1.8
i 0.4 e.v.
