  Reaction-diffusion equation model for a 2-dimensional gas discharge system is
introduced in close relationship with the recent experiment by Nasuno. The
model shows formation of spots, molecule-like organization of a cluster of
spots, moving of spots, and intermittent collapse and recreation of spots, in
agreement with experiments. The pattern dynamics are classified into
distributed, localized, and moving spots, and periodic wave pattern. The phase
diagram displayed against the current and pressure has some agreement with that
observed in the experiment. Dynamic change of spot numbers as well as the
structure of the spot cluster is studied in terms of the collective flow of
charge, and discussed as chaotic itinerancy.
