# Why is a third body needed in the recombination of two hydrogen atoms?

In the article Discuss. Faraday Soc. 1962, 33, 205, the authors say that in order to form molecular hydrogen from collision to atom we need a third body to remove the excess energy. That is we have the reaction $$\ce{H + H + M -> H2 + M}$$.

I suppose the reason is because if we have the excess this energy will break the bond. If it this the case why the energy can not be transferred to the electron and so would have $$\ce{H + H -> H2^*}$$, where $$\ce{H2^*}$$ denotes an excited state of $$\ce{H2}$$?

• You can use the \ce{...} macro to typeset chemical equations; it's easier and also provides the correct output (chemical symbols should be upright, not in italics). Check out my edit for some examples. – orthocresol Dec 1 '20 at 19:18
• An excited state of H2 would still have the excess energy. – Ivan Neretin Dec 1 '20 at 19:22
• Temperature is irrelevant. Or I'd better put it this way: the rest of the gas might be as cold as you like, but this one molecule that has just formed from two atoms is very, very hot. – Ivan Neretin Dec 1 '20 at 19:32
• All right, speaking of the heat of one molecule is an abuse of language. Would it be better if I said that it has very high energy? – Ivan Neretin Dec 1 '20 at 19:37
• @amiltonmoreira - what is the binding energy of H2? – Jon Custer Dec 1 '20 at 20:02