The transport of H-2 in liquid water is studied using adiabatic, nonadiabatic, and classical molecular dynamics methods in an attempt to understand the influence of transitions between translational states of the H-2 molecule driven by solvent fluctuations. Quantum autocorrelation functions of the H-2 Center-of-mass velocity are computed in various dynamical limits. We find that there are strong nonadiabatic couplings between the instantaneous adiabatic translational states of H-2 in water which result in rapid decorrelation of the H-2 center-of-mass velocity for the time evolving translational mixed state. Transitions to excited translational states reduce the effects of caging dynamics in the velocity autocorrelation function dramatically Classical and adiabatic descriptions of the dynamics predict that caging is much more important than we find nonadiabatically. Diffusion constants and frequency spectra are compared for the different limits and with experiment.