An alternative approach to condensed-phase photoionization

Starting from Maxwell's equations for the electromagnetic field in a linear Kramers-Kronig dielectric, a general expression for photoionization cross sections of atoms or molecules embedded in a medium and a dielectric influence function (DIF) are derived in this Letter firstly. It is also suggested that a density turning point (DTP) of a photoionization process may be viewed as the critical density Nc(ω) where the photoionization properties may have notable and different variations with density.