The sticking probability (s) of the CN(X-2 Sigma(+)) radicals onto the hydrogenated amorphous carbon nitride (a-CNx:H) films was determined by measuring the density of CN(X-2 Sigma(+)) in the gas phase, the flow speed, and the weight of a-CNx:H. The CN(X-2 Sigma(+)) radicals were produced by the dissociative excitation reaction of BrCN with the microwave discharge flow of Ar, and were observed by the laser induced fluorescence (LIF) spectroscopy of the CN(A(2)Pi-X-2 Sigma(+)), 4-0, 5-1, and 7-2 bands. The LIF intensity was calibrated against Rayleigh scattering intensity by Ar atoms, from which the density of CN(X-2 Sigma(+)) was determined as 1.0 x 10(18) -4.9 x 10(18) M-3 depending on the pressure of Ar (P-Ar) as 0.4-0.7 Torr. The s value was in the range of 0.032-0.019 which was also dependent on PAr. According to the IR observation of the a-CNx:H films, the P-Ar-dependence of s was found to originate in the reactivity of the CN radicals on the film surface. (c) 2005 Elsevier B.V. All rights reserved.