The resulting approach can be useful in the field of astrochemistry to produce effective and sufficiently accurate approximations for quasi-thermodynamic modeling of the interstellar medium, interplanetary environment, and atmospheres of exoplanets, to include the possibility of polycationic states in the photochemistry of molecules and molecular clusters under the influence of harsh radiation. As a perspective, the proposed approach can be extended to include the higher-order terms of the energy expansion (Equation ), vibrational effects, and reach a more accurate approximation of thermodynamic potentials (enthalpy, entropy, free energies).