The radical-radical reaction dynamics of ground-state atomic oxygen [O(P-3)] with propargyl radicals (C3H3) has first been investigated by applying laser induced fluorescence spectroscopy in a crossed beam configuration, together with ab initio calculations. A new exothermic channel of O(P-3)+C3H3-->C3H2+OH was identified and the nascent distributions of OH reaction product in the ground vibrational state (X (2)Pi:v"=0) showed substantial rotational excitations with an unusual bimodal feature composed of the low- and high-N" components. No spin-orbit propensities were observed, whereas the averaged ratios of Pi(A('))/Pi(A") were determined to be 0.60+/-0.28. With the aid of the CBS-QB3 level of ab initio theory it is predicted that on the lowest doublet potential energy surface the reaction proceeds through the addition complexes formed through the barrierless addition of O(P-3) to C3H3, and that the counterpart of C3H2 of the probed OH product is cyclopropenylidene ((1)c-C3H2). On the basis of the comparison with statistical prior and rotational surprisal analyses, the ratio of population partitioning for the low- and high-N" regimes is estimated to be about 1:2 and the reaction is described in terms of two competing addition-complex mechanisms: a major short-lived dynamic complex in the high-N" regime and a minor long-lived statistical complex in the low-N" regime. (C) 2003 American Institute of Physics.