Biradicals 2S and 2T thermo and reactivity

[rwest]

Noticed this when importing USC-Mech-ii.
RMG predicted some reactions that matched USC-Mech reactions, and created a H2CC species:

1 C 0  {2,D}
2 C 2T {1,D}

But the USC thermo is for the singlet:

1 C 0  {2,D}
2 C 2S {1,D}

Which is much more stable.
The DFT_QCI_Thermo database has both singlet and triplet in.
I am not sure what the reaction should make.

Probably we should have a state-crossing reaction, a bit like the 1,2-Birad_to_alkene family, that reacts H2CC(T) + M <=> C2CC(S) + M.

There may be other issues though - I'm not sure when RMG makes a 2T and when a 2S, nor am I sure if they are equally reactive in terms of matching nodes in reaction families.

See also:

• issue radicals exported incorrectly to Java #18.
• http://dx.doi.org/10.1063/1.1456508

[rwest]

@nyee is this cleared up in pull request #38?

[nyee]

No, we were mostly just trying to eliminate R!H {2S,2T}, which is impossible to in the new style adj lists.

Other than in statmech, we didn't change anything that had to do with specifically with C radicals. The statmech we made all 2T because we were able to find the original source and it looked unlikely that anything had to do with singlets.

Definitely don't have a state-crossing reactions yet.