HX rotational state distributions following vibrational predissociation (VP) of C2H2-HX (X = Cl, F, O) chillers are predicted by expressing the predissociation process as the joint probability of rovibrational excitation in the fragments following "Internal collision" ill the vibrationally excited dimer. Calculations of these Joint probabilities for the T-shaped chillers of acetylene with HCl, DCl, HF, and OH using the angular momentum (AM) method reproduce experimental distributions With reasonable accuracy In dimers of this complex, many different pathways for the disposal of initial energy and momentum exist in principle. The Use Of simple physical arguments based oil (it) the direction of initial impulse upon excitation and (b) restricted relative geometries due to limited amplitude of relative Motion of the dimer component, allows the number of effective dissociation pathways to be much reduced. For these, (lie probability of rotational and rovibrational transfer into the fragments is calculated. a process that generally involves summing, over a number C2H2 rovibrational; states for each value of J(ux) In calculating relative rotational populations in the fragments, it Was found essential 10 must calculate the threshold value of available energy lot that transition and the threshold value of b(n), the effective impact parameter without these modifications, channels of lowest J(UX) and/or j(C2H2) dominate, which generally is not found experimentally. The need For these modifications is attributed 10 energy conservation in the dissociation and (lie limited range of relative Orientations that the chiller pair call explore The AM method I,; able to predict the very different fragment rotational excitations in this series of dimers family well using, only readily available data in addition, I number of new insights Into the physical principles that control the dissociation of molecule-molecule dimers have emerged and are discussed The results; suggest that each fragment quantum state pair results from a very specific relative geometry Very Specific relative geometry of dissociation and that the balance between vibrational and rotational excitations is determined by the requirement to restrict the angular momentum "load" in the predissociation.