Photo-predissociation dynamics of rotational states (N') of OH (A (2)Sigma(+),nu'=3 and 4) are studied using high-n Rydberg atom time-of-flight technique. Spin-orbit branching fractions of O(P-3(J=2,1,0)) are measured: 0.676+/-0.010:0.138+/-0.013:0.186+/-0.017 for N'=0 in nu'=3 and 0.873+/-0.026:0.102+/-0.028:0.025+/-0.005 for N'=0 in nu'=4, in excellent agreement with the recent theory. While OH A (2)Sigma(+) nu'=3 predissociates predominantly via a single (4)Sigma(-) state, nu'=4 decays via the (4)Sigma(-), (2)Sigma(-), and (4)Pi states, and interferences of these dissociation pathways strongly influence the O(P-3(J)) fine-structure distributions. D-0(O-H)=35 565+/-30 cm(-1) is obtained. (C) 2003 American Institute of Physics.