CN(X2 Sigma+) radicals were produced from the dissociative excitation reaction of CH3CN with the microwave discharge flow of Ar. The mechanism of the production of these radicals was studied on the basis of a combined analysis of the laser-induced fluorescence (LIF) and electrostatic-probe measurements. The densities of CN((XI)-I-2 (+)) pound and the metastable states of Ar, Ar(P-3(0,2)), were determined by observing the LIF spectra of the CN(A(2)I (i)-(XI)-I-2 (+)) pound, Ar(P-3(1)-P-3(2)), and Ar(P-3(1)-P-3(0)) transitions. A chemical-kinetic analysis of the above densities together with the temperature and the density of free electrons was carried out to elucidate that the dominant mechanism of the production of CN((XI)-I-2 (+)) pound is the energy transfer from Ar(P-3(0,2)). The rate constant of the production of CN((XI)-I-2 (+)) pound is determined to be (4.6 +/- A 0.4) x 10(-17) m(3) molecule(-1) s(-1). Based on the results of the present and our previous studies (Ito et al. in Diam Relat Mater 24:121-125, 2012) , a quantitative description was made on the incorporation of N atoms into hydrogenated amorphous carbon nitride films formed in the present reaction system.