The photolysis of mercury diethyl vapour has been investigated in a static system over a pressure range of 0 to 80 mm. and a temperature range of 75 to 200° C. The products were analyzed for C
2
H
6
, C
2
H
4
, C
4
H
10
, C
4
H
8
. No significant amounts of H
2
, CH
4
, C
4
H
8
or higher hydrocarbons were found. Rotating sector experiments have enabled a complete determination of the velocity constants of the reactions: (1) C
2
H
6
+ C
2
H
5
= C
2
H
4
+ C
2
H
6
, (2) C
2
H
5
+ C
2
H
5
= C
4
H
10
, (3) C
2
H
5
+ Hg
Et
2
= C
2
H
4
+ C
2
H
6
+ Hg + C
2
H
5
. Energies of activation and frequency factors for these reactions have been deduced.
E
1
–
E
2
= 0⋅8±0⋅2 kcal./mole,
E
2
≯ 0⋅65 kcal./mole has been deduced from
k
2
at 150° C and the calculated collision frequency.