The energy of the quasi-free electron in near critical point H$_2$, D$_2$ and O$_2$*

Field enhanced photoemission is used to measure the density ($\rho$) dependent quasi-free electron energy $V_0(\rho)$ in the repulsive fluids H$_2$ and D$_2$, and the attractive fluid O$_2$, for the first time. $V_0(\rho)$ in each of these fluids was obtained from low density to the density of the triple point liquid, at noncritical temperatures and on an isotherm near the critical isotherm. A novel critical point effect is observed in each of the fluids and is accurately explained by the local Wigner-Seitz model with the selection of appropriate intermolecular potentials for each fluid.