The gas equation of state may be one of the critical factors for the disk instability theory of gas giant planet formation .
This letter addresses the treatment of H _ { 2 } in hydrodynamical simulations of gravitationally unstable disks .
In our discussion , we point out possible consequences of erroneous specific internal energy relations , approximate specific internal energy relations with discontinuities , and assumptions of constant \Gamma _ { 1 } .
In addition , we consider whether the ortho/para ratio for H _ { 2 } in protoplanetary disks should be treated dynamically as if the species are in equilibrium .
Preliminary simulations indicate that the correct treatment is particularly critical for the study of gravitational instability when T = 30 - 50 K .