Singlet molecular oxygen excites iodine to almost every vibrational level of the B (3)Pi(0+u) state. deduced that the first step involves excitation to the A (3)Pi(1u) state of I-2 by O-2 (1)Sigma(+)(g) with subsequent excitation by O-2 (1)Delta(g) or O-2 (1)Sigma(+)(g).