Beginning with Paterson 1981 [] we find
where
where 
J/mol-
K is the gas constant, and Q for
temperatures less than -10 
C is in the range 42-84 KJ/mole, with a
usable value of 60 KJ/mole []. For temperatures greater
than -10 
C, Q appears to depend on temperature, but a value of 139
KJ/mole is given.