Singlet Molecular Oxygen and Superoxide Radical Anion

Singlet molecular oxygen generated photochemically by rubrene sensitization or by direct excitation in a microwave-discharged stream of oxygen at low pressure is physically quenched by superoxide radical ion in aprotic media, with a quenching rate k_q = 3.6 ± 0.1 × 10⁷ M^?1 s^?1.