Singlet—triplet separation

The calculated heat of formation of singlet carbene agrees well with experiment. That of triplet carbene is not known. The ionization potential of singlet carbene, determined spectroscopically 51 (10.26 eV) is much less than the electron impact value S3 (11.9 eV) if the latter refers to triplet carbene, as seems likely, the singlet-triplet separation is 1.64 eV or 37.8 kcal/mole, which is quite close to our estimate (28.5 kcal/mole). 

Aside from the preceding argument based on the oxygenation kinetics, no quantitative experimental estimates of the singlet-triplet separation in TMB have been reported. If a suitable precursor of the TMB radical anion in the gas phase can be made, photodetachment PES of TMB would become a likely way to solve this problem. 

We see that there are two possible limits for H2 + 0- We take the one of lower energy as appropriate and this will depend on the H—H separation. The D—separation of the oxygen atom is 1.958 eV and calculations by Kolos and Wolniewicz 136) show that the singlet-triplet separation of H2 is equal to this at 1.669 A. Thus the two-body potential that we use in (53) will be the singlet state potential for... 

We conclude this rather lengthy survey with a simple example the application of different basis sets to the singlet/triplet separation in the CH2 radical [66], which was used as a comparison of iV-particle space treatments in Sec. 3.2. 

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