Collisional quenching of the NO C2P (v = 0) and D2S+ (v = 0) levels by Ar was studied by means of synchrotron radiation at ACO (Orsay). A depopulation rate of D(O) by Ar was derived; it is in good agreement with previous studies. The C(0) fluorescence shows an anomalous behavior with quencher pressure, which is accounted for by a pressure-induced decrease in the rate of predissocn. [on SciFinder (R)]