The Low Lying States of Phenylnitrene and Phenylcarbene

The results of a number of ab initio computations of 2 are listed in Table 5.3. In all the cases, the triplet is predicted to be the ground state, in accord with experiment. CASSCF predicts an energy difference of about 10 kcal mol and correction for dynamic correlation increases the gap. These values 

TABLE 5.3 Singlet-TViplet Energy Gap (kcal mol ) of Phenylcarbene (2) 

5 kcal mol-i (CASPTZN ), or 15.9 kcal mol (MR-A(3CC ). The initial experimental determination via negative ion photoelectron spectroscopy suggested a singlet-triplet gap of 18 2 kcal mor. Wenthold reexamined the spectra of phenylnittene anion and suggests that the gap is somewhat smaller, 

5 kcal mol . The more recent CCSD and MR-AQCC computations are in good accord with this revised estimate. The next lowest singlet state is the Aj state dominated by the configuration that doubly occupies the in-plane orbital (8 2) ibis state is about 30 kcal mol above the triplet.  

TABLE 5.4 Singlet-Triplet Energy Gap (kcal mol of Phenylnitrene (1) 

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