Species formed in the reactions of Ta + and TaO + with ethene are examined spectroscopically using infrared multiple photon dissociation (IRMPD) action spectroscopy. Ta + , TaC2H2 + , and TaO + are all observed to dehydrogenate ethene yielding [Ta,2C,2H] + , [Ta,4C,4H] + , and [Ta,O,2C,2H] + , respectively. For these species, IR action spectra are obtained in the 225 -3400 cm -1 range by monitoring fragmentation into the [Ta,2C] + , [Ta,4C,nH] + (n = 2, 3), and [Ta,O] + mass channels, respectively. The spectra are assigned to TaC2H2 + , Ta(C2H2)2 + , and OTaC2H2 + metallacyclopropene species on the basis of comparisons with scaled vibrational spectra from B3LYP/def2-TZVPPD geometry optimized structures. To further elucidate the chemistry observed, complete reaction coordinate pathways having quintet, triplet, and singlet spin for all three dehydrogenation reactions have also been examined.