The reaction process of the production of CrOH(C2H4)(2)(+) was studied in connection with the ethylene polymerization on a silica-supported chromium oxide catalyst (the Phillips catalyst). Cluster ions CrOH(C2H4)(+) and CrOH(C4H8)(+) were produced by the reactions of CrOH+ with C2H4 (ethylene) and C4H8 (Ibutene), respectively, and were allowed to collide with a Xe atom under single collision conditions. The cross section for dissociation of each parent cluster ion was measured as a function of the collision energy (collision-induced dissociation, or CID). It was found that (i) the CID cross section for the production of CrOH+ from CrOH(C2H4)(2+) increases sharply at the threshold energy of 3.16 +/- 0.22 eV and (ii) the CID cross section for the production of CrOH+ and C4H8 from CrOH(C4H8)(+) also increases sharply at the threshold energy of 3.26 +/- 0.21 eV. In comparison with the calculations based on a B3LYP hybrid density functional method, it is concluded that two ethylene molecules in CrOH(C2H4)(2+) are polymerized to become 1-butene. The calculation also shows that the dimerization proceeds via CrOH(C2H4)(+) (ethylene complex) and CrOH(C2H4)(2)(+) (ethylene complex), in which the ethylene molecules bind with CrOH+ through a pi-bonding.