This talk will highlight recent work in our group in which we use Diffusion Monte Carlo approaches to study molecular vibrations of several fluxional systems. The molecular systems that will be the focus of the talk will be CH5+ and ion-water complexes. For these studies, we focus on two approaches. The first involves a fixed-node treatment of rotationally and vibrationally excited states. This approach enables us to evaluate the "zero-order bright state" associated with a particular molecular vibration. The results of these calculations include the frequency of the state of interest as well as the associated probability amplitude. A second approach will be described in which we re-express the excited state energy as an expectation value over the ground-state wave function. The results of these approaches are promising.