Energy of the quasi-free electron in hydrogen, deuterium and oxygen: Probing intermolecular potentials within the local Wigner-Seitz model*

We present for the first time the quasi-free electron energy $V_0(\rho)$ for H$_2$, D$_2$ and O$_2$ from gas to liquid densities, on noncritical isotherms and on a near critical isotherm in each fluid. These data illustrate the ability of field enhanced photoemission (FEP) to determine $V_0(\rho)$ accurately in strongly optically absorbing fluids (e.g., O$_2$) and fluids with extremely low critical temperatures (e.g., H$_2$ and D$_2$). We also show that the isotropic local Wigner-Seitz model for $V_0(\rho)$ -- when coupled with thermodynamic data for the fluid -- can yield optimized parameters for intermolecular potentials, as well as zero kinetic energy electron scattering lengths.