For Velasco et al.'s purposes, the state of a molecule is totally defined by its
location and momentum, and the state of an ensemble of molecules is the combination of the individual molecules» states: for an ideal - gas ensemble consisting of N monatomic molecules, each of which is characterized by x, y, and z components both of position and of momentum, the ensemble's state can be represented by a point
in 6N space,
in which a surface I think of as a hyperparaboloid represents the states that exhibit a
given total (potential + kinetic)
energy.