There is no strict distinction between physicochemical and physical research methods. However, physical methods usually refer to many, especially modern methods developed by physicists and used in chemistry. These methods, of course, do not include such methods as separation by distillation, recrystallization, weighing, determination of melting and boiling temperatures, purely thermochemical and electrochemical methods, etc.

The physical method is based on the interaction of incident radiation, particle flux or any field with the substance and measuring the result of this interaction. If we designate the measured physical property as x, and the incident radiation as I0 , then the result of the interaction I(x) will contain information about the property x. I0 and I can be of the same nature, such as X-rays falling on crystal I0 and scattered by crystal after interaction I(x), where x is crystal structure. The direction of arrows from block I0 to block x shows the propagation of radiation from the source to the object under study. The arrow from block x to block I(x) means the result of interaction if the physical law of this interaction is known and the physical property x is known. Such sequence means the direct task of physical method.

But the researcher is also interested in the inverse problem: to find the property x by the result of interaction. In a certain sense these are two different problems, and it is not always the case that knowing the solution to the forward problem gives the solution to the inverse problem. The solution to the inverse problem determines the capabilities of the method, its sensitivity. In cases when the inverse problem has a stable solution, such a problem is said to be correctly formulated. The stability of the solution implies a small influence of small deviations in I(x) on the value x. The defined physical property x can be of different nature: interatomic distances or coordinates of atoms, which can be symbolically denoted by r, sets of frequencies of vibrations of atoms in the molecule or sets of frequencies of electron transitions etc.

The vertical block system of the scheme shows that some physical properties can be calculated theoretically on the basis of classical physics or quantum mechanics. Since any physical theory relies on a certain model of a molecule or substance, the comparison of theory and experiment allows to verify the model, i.e. theoretical constructions.

The upper block corresponds to the set of chemical properties of a molecule or substance in the concepts of the theory of chemical structure, which are mentioned above. Due to the fact that on the basis of the physical property x it is possible to estimate some chemical properties, as, for example, by the length of carbon-carbon bond to determine its multiplicity, then accordingly, knowing the chemical structure, it is possible to predict some physical properties.