The ultimate level of understanding of chemical reactions is achieved by solving quantum mechanical equations describing intermolecular collisions. This is scattering theory. The computations can be difficult and time-consuming, and the resulting data can be numerous and difficult to interpret. My interest is in relating the results of quantum mechanical scattering calulations (ultimately state-to-state or channel-to-channel reaction probabilities) to a phenomenological understanding of chemical reaction, that is, to dynamical features of the reactive flux and to approximate theories of reaction such as transition state theory. My collaborators and I have related chemical reactivity (thermal rate constants) to quantized transition states for several atom-diatom collisions. My current efforts regard the reaction of D with H2, an isotopolog of the fundamental bimolecular reaction (that of H with H2). I am investigating the reformulation of a separable rotation approximation for the thermal rate constant in terms of quantized transition state levels, and the fine characterization of the quantized transition state in terms of vibrational and rotational constants.