We derive a closed-form expression for the angular momentum polarization (polarization parameters) of the velocity distribution of the AB(v’,J’) product formed by the reaction sequence AX + hv --> A + X followed by A + BC(v,J) --> AB(v’,J’) + C. Although in general (2J’ + 1)2 parameters are needed to describe the polarization of an arbitrary ensemble of diatomic molecules in a rotational state J’, we show that the polarization of the velocity distribution of the AB(v’,J’) product can be completely specified by 5J’ dynamically significant polarization parameters. This reduction in the number of degrees of freedom is achieved by introducing a frame of reference we call the stationary-target frame. If the correlation between the relative velocities of the reactants and products and J’ is described with respect to this frame, the polarization-dependent velocity distribution may be written in terms of the 5J’ polarization-dependent state-to-state differential cross sections d sigma(k0)/d Omega(r), (k even), d sigma(kl)/d Omega(r), and d sigma(k2)/d Omega(r), for which 0 less than or equal to k less than or equal to 2J’.