The reaction of V atoms with H2O and various concentrations of C2D4 in argon has been investigated by matrix isolation infrared (IR) spectroscopy. Both C2D6 and CD2H-CD2H are observed as the major products of a set of parallel processes involving hydrogenation of ethene where the formal source of hydrogen is either CA or H2O. Portions of the IR spectrum of CD2H-CD2H isolated in an argon matrix are observed for the first time. For experiments involving low concentrations of CA, irradiation of the matrix with light of wavelengths >455 nm results in VH2 formation, with limited observation of ethene hydrogenation. The source of H-2 is believed to be due to photoelimination of molecular hydrogen from HO-V-H species, during matrix deposition, with OV as an additional product. Recombination of OV with available H-2 in the matrix is proposed as the source of OVH2 under low ethene conditions. No evidence for VD2 formation is observed under our conditions. At higher CA concentrations, VH2 formation is suppressed, while products of ethene hydrogenation are maximized. A second process competing with H-2 elimination in which HO-V-H reacts with CA is proposed. Parallel reaction schemes involving V atom insertion into the O-H bonds of water or the photoinduced insertion of V atoms into the C-D bonds of CA are proposed to account for the observed hydrogenation products. In each mechanism, insertion of CA into the V-H or V-D bonds of transient intermediates is followed by photoinduced elimination of the associated ethane isotopomer.