The oscillator strength was calculated for the vinyl radical at MRCISD and CASSCF levels between the ground state and several doublet excited states. Results indicated that the (C) over tilde (2)A' <-- (X) over tilde (2)A' transition, of pi* <-- pi character that was usually thought to be strong, was very weak. The (C) over tilde (2)A' state is the result of coupling between the pi* <-- pi triplet excitation and the nonbonding electron, and the transition is essentially 'spin-forbidden'. Another high-energy doublet state was found with strong transition from the ground state arising from coupling between the pi* <-- pi singlet excitation and the nonbonding electron. This appears to be a common feature for pi* <-- pi excitation in a radicals. (C) 2002 Elsevier Science B.V. All rights reserved.