Collisional reactions of CH3CN, C2H5CN, and n-C3H7CN with argon metastable atoms, Ar-m, were investigated by observing the CN violet emissions in a flowing afterglow under essentially collision-free conditions. Rovibrational distributions of CN(B-2 Sigma(+)) were determined by a simulation analysis of the main band of the CN(B-2 Sigma(+)-X(2) Sigma(+)) emission spectra. The obtained vibrational distribution was compared with that predicted by the statistical theory. The effective degree of freedom of vibration involved in the available energy disposal was found to increase with the length of the hydrocarbon chain of the target molecule. This increase supports that CN(B-2 Sigma(+)) is produced via energy transfer. The reaction cross sections for the dissociative excitations which produce CN(B-2 Sigma(+)) from CH3CN, C2H5CN, and n-C3H7CN with Ar-m were determined to be 1.0(1), 0.8(1), and 0.6(1) Angstrom(2), respectively, by using the reference reaction method. The decrease in the reaction cross section with respect to the length of the hydrocarbon chain is attributable to the steric hindrance of the molecular orbital from which the excitation leads to the effective production of the CN(B-2 Sigma(+)) by the inert hydrocarbon chain and/or the dissipation of available energy to the hydrocarbon chain.