Electronic States of Trimethylenemethane

Ab initio generalized valence bond (GVB) and configuration.interaction (CI) calculations were carried out on the planar and bisected forms of trimethylenemethane. The results indicate that the ground state is the planar triplet with the planar singlet state 26 kcal/mol higher. The rotational barrier for the triplet state is 18 kcal/mol, while one component of the planar singlet prefers the bisected geometry by 7 kcal/mol. We predict the transitions for the chemically interesting states as fol-lows: planar triplet, λmax 266 nm with f = 0.002; bisected singlet, λmax; 359 nm with f = 0.0008; and planar singlet, λmax 289 nm with f = 0.10. The vertical ionization potential is calculated as 8.3 eV.