We report the effects of collision energy (E-col) and five different H2CO+ vibrational modes on the reaction of H2CO+ with C2D4 over the center-of-mass E-col range from 0.1 to 2.1 eV. Properties of various complexes and transition states were also examined computationally. Seven product channels are observed. Charge transfer (CT) has the largest cross section over the entire energy range, substantially exceeding the hard sphere cross section at high energies. Competing with CT are six channels involving transfer of one or more hydrogen atoms or protons and one involving formation of propanal, followed by hydrogen elimination. Despite the existence of multiple deep wells on the potential surface, all reactions go by direct mechanisms, except at the lowest collision energies, where short-lived complexes appear to be important. Statistical complex decay appears adequate to account for the product branching at low collision energies, however, even at the lowest energies, the vibrational effects are counter to statistical expectations. The pattern of E-col and vibrational mode effects provide insight into factors that control reaction and interchannel competition. (C) 2004 American Institute of Physics.