An Arrhenius-type plot (Figure ) was constructed for reactions of 1a or 3 with TEMPO monitored by photo-NMR spectroscopy (440 nm LED) at six different temperatures. The calculated activation energies for these reactions were Ea = 4 kcal/mol and 3 kcal/mol for 1a and 3, respectively. The similarity of these small energy barriers for Pd(II)-C cleavage at the excited state therefore do not account for the observed differences in quantum yield between the two types of organo-Pd complex. Additional computational and spectroscopic investigations were informative in parsing other possible origins of efficiency differences.