An optically pumped IF laser operating on the B Jll(O+)-+X II + transition has been studied. Vibrational levels v' = I, 2, 3, 4, 5, and 6 of IF(B) were pumped by a dye laser pulse and lasing was observed both from the level pumped and from lower levels populated as a result of collisions with bath gas molecules. Time delays from 0.5 to 3.0 J.t s were observed between termination of the pump pulse on v' = 5 and lasing out of v' = O. The longer delays result from slower vibrational relaxation at lower pressures. The stable nature of v' = 0 reservoir indicates that the B -X electronic transition is very attractive as a potential chemical laser system.