NCO radicals were produced by laser photolysis of CHBr3 at 266 nm followed by the reaction of CH with N2O. The radicals were then electronically excited from the ground electronic state to the A (2)Sigma(+) state with a Nd:YAG laser pumped dye laser at 438.6 nm in the Q subband of A (2)Sigma(+)(00(0)0)<--X (2)&UPi;(i)(00(1)0). The rate constants k(q) and thermally averaged cross sections σ(q) for collision quenching of NCO (A (2)&USigma;(+)) by n-CnH2n+2 (n=1,5-8), c-C6H12, CH4-nCln (n=1-4), CH3OH, CH3NO2, and CCl2F2 were measured at room temperature (298 K) by observing the time-resolved fluorescence signals of the excited NCO in a cell at total pressure of about 20 Torr. Formation cross sections of complexes of the electronically excited NCO radicals and quenchers were calculated by means of a collision complex model. It was shown that the quenching rates of NCO (A (2)&USigma;(+)) by alkane molecules increase with the number of C-H bonds of the molecules, and that the attractive forces play a main role in the collisional quenching processes of NCO (A (2)&USigma;(+)) by the quenchers studied in this work. (C) 2003 American Institute of Physics.