The three-body ionic-recombination reaction of Ar+(P-2(3/2))/Cl-/Ar leading to ArCl(B,C),Ar(P-3(2)), and Cl(4s,4s’,4p,4p’,4d,5p,6s) has been studied spectroscopically in an Ar flowing afterglow. The results obtained are compared with our previous data for the Ar+(P-2(3/2))/Cl-/He reaction in order to examine the effects of the third-body atom. The Ar+(P-2 (3/2))/Cl-/Ar reaction populates lower energy states of [Ar+(P-2(3/2)Cl-] intermediates than the Ar+(P-2(3/2))/Cl-/He one, so that the branching ratio of excimer becomes large in comparison with those of predissociation channels, the lower ArCl(B) state is preferentially excited than the ArCl(C) state, the ArCl(B) state is populated in lower vibrational levels, and the electronic state distribution of Cl* shifts to lower energy. On the basis of these findings, it is concluded that the heavy Ar atom is a more efficient acceptor of the excess energy than the light He atom in the Ar+(P-2(3/2))/Cl-/Rg (Rg=rare gas) system.