  We investigate the dissociation and ionization equilibria of deuterium fluid
over a wide range of temperatures and densities. The partition functions for
molecular and atomic species are evaluated, in a statistical-mechanically
consistent way, implementing recent developments in the literature and taking
high-density effects into account. A new chemical model (free energy function)
is introduced in which the fluid is considered as a mixture of diatomic
molecules, atoms, ions and free electrons. Intensive short range hard core
repulsion is taken into account together with partial degeneracy of free
electrons and Coulomb interactions among charged particles. Samples of
computational results are presented as a set of isotherms for the degree of
ionization, dissociated fraction of molecules, pressure, and specific internal
energy for a wide range of densities and temperatures. Predictions from the
present model calculations show an improved and sensible physical behavior
compared to other results in the literature.
