Three types of experimental data are presented for the benzyl radical/ethylene molecular cluster mass-resolved excitation spectra (MRES), ionization energy threshold determination, and excited-state lifetime measurements at different excitation energies. MRES of benzyl radical (C2H4)(1),(2) exhibit broad features in the D-1 <-- D-0 benzyl radical absorption region that extend beyond 11 810 cm(-1) of vibrational energy in D-1. The ionization threshold for the one-to-one cluster is shifted by -1 160 cm(-1) relative to that of the bare benzyl radical. Cluster excited-state lifetime measurements indicate a shortened lifetime at higher excitation energy. This collection of benzyl radical/ethylene data differs greatly from that of the previously studied benzyl radical/ethane cluster system. These latter results consist of well-resolved spectroscopic structure with low-energy van der Waals modes and molecular vibrations, a small shift in ionization energy relative to the bare benzyl radical of similar to -50 cm(-1), and vibrational predissociation at roughly 700 cm(-1) of vibrational energy in D-1. The anomalous benzyl radical/ethylene data can be explained if one postulates that an excited-state bimolecular addition chemical reaction occurs between benzyl radical and ethylene upon optical excitation of the benzyl radical (D-2, D-1 <-- D-0) Ab initio calculational results are presented which support the assertion of an apparent excited-state chemical reaction. Finally, unimolecular dissociation rate theories are used to extract an excited-state "binding energy" for the benzyl radical/ethylene "cluster" from excited-state lifetimes.