The Electronic States of Linear Methylene

The electronic energy levels of the linear methylene radical, with r(C—H) = 1.0295 Å, have been calculated by the LCAO/MO/CI procedure. The state of lowest energy has 3 ∑ g − symmetry, and is accompanied by low-lying 1 Δ g and 1 ∑ g + states. Allowed intravalence shell transitions from the ground state ( 3 Π u − 3 ∑ g − ,− 3 ∑ u − − 3 ∑ g − ) are too high in energy to account for the observed transition at 8.6 ev, indicating that the latter is of Rydberg type if it is between linear combining states.