The photoinitiated unimolecular decomposition of formaldehyde via the H + HCO radical channel has been examined at energies where the S-0 and T-1 pathways both participate. The barrierless S-0 pathway has a loose transition state (which tightens somewhat with increasing energy), while the T-1 pathway involves a barrier and therefore a tight transition state. The product state distributions which derive from the S-0 and T-1 pathways differ qualitatively, thereby providing a means of discerning the respective S-0 and T-1 contributions. Energies in excess of the H + HCO threshold have been examined throughout the range 1103 less than or equal to E dagger less than or equal to 2654 cm(-1) by using two complementary experimental techniques; ion imaging and high-n Rydberg time-of-flight spectroscopy. It was found that S-0 dominates at the low end of the energy range. Here, T-1 participation is sporadic, presumably due to poor coupling between zeroth-order S-1 levels and T-1 reactive resonances. These T-1 resonances have small decay widths because they lie below the T-1 barrier. Alternatively, at the high end of the energy range, the T-1 pathway dominates, though a modest S-0 contribution is always present. The transition from S-0 dominance to T-1 dominance occurs over a broad energy range. The most reliable value for the T-1 barrier (1920 +/- 210 cm(-1)) is given by the recent ab initio calculations of Yamaguchi It lies near the center of the region where the transition from S-0 dominance to T-1 dominance takes place. Thus, the present results are consistent with the best theoretical calculations as well as the earlier study of Chuang , which bracketed the T-1 barrier energy between 1020 and 2100 cm(-1) above the H + HCO threshold. The main contribution of the present work is an experimental demonstration of the transition from S-0 to T-1 dominance, highlighting the sporadic nature of this competition.