A quasi-static method is developed for measuring the deactivation rate constants of O-2(a(1)Delta(g)) in gas phase by monitoring its IR radiation decay via a flow-stop technique. This method has taken into account the energy-pooling reaction of O-2(a(1)Delta) and thus suits fairly high O-2(a(1)Delta) concentration without identifying its absolute value, leading to simpler operation and higher signal/noise ratio. Utilizing this method, the O-2(a(1)Delta) deactivation rate by D2O is for the first time measured to be 2.10 +/- 0.18 x 10 (18) cm(3) s (1), while those for O-2(X-3 Sigma(-)(g)), H2O, H-2 and D-2 are found to agree well with the data in literature. (C) 2011 Elsevier B.V. All rights reserved.