What They Saw
They extracted nitrogenase from Azotobacter vinelandii. ATP was necessary for any activity, of course; 3 mM was the optimal amount in their in vitro reactions, possibly because of the amount of magnesium ions that were present (5 mM). They saw 1.6 hydrogens per nitrogen fixed, on average, a bit higher than the normal figure of 1; about 33% of the energy flux went to hydrogen (normal figure is 25%).
With azide added, 1 mole azide is made into 1 mole ammonia and 1 mole dinitrogen. Lower levels allowed production of hydrogen instead, but that wasn't investigated much. The same was true with acetylene; both seem better substrates than nitrogen.
Cyanide is reduced to methane and ammonia; optimal concentrations were 2-4 mM. At other concentrations, there are other products formed: ethylene, ethane, methylamine (CH3NH2). They don't discuss hydrogen.
However, their calculations of ATP per electron pair transferred were skewed because they didn't measure all the products (i.e. hydrogen gas).