Thin films of 4-quaterphenyl (4-QP) are thermally deposited in an ultrahigh vacuum on polycrystalline gold and oxidized silicon substrates. In the process of deposition, the structure of unoccupied electron states 5-20 eV above the Fermi level (E-F) and the surface potential are monitored by the method of total current spectroscopy (TCS) using an incident beam of low-energy electrons. During the deposition, the electron work function of the surface changes because of a change in the surface layer composition, reaching a steady-state value of 4.+/- 0.1 eV at a 4-QP film thickness of 8-10 nm. The density of valence states (DOVS) and the density of unoccupied states (DOUS) in model 4-QP films are calculated using the linearized augmented plane wave method in the generalized gradient approximation of the density functional theory. In the model 4-QP structure, the minimal spacing between carbon atoms of neighboring 4-QP molecules is taken to be 0.4 nm in order that intermolecular interaction can be assumed to be relatively weak, which is observed in disordered 4-QP films. The TCS-measured DOUS and the DOUS predicted theoretically are in good agreement.