In this paper, the dispersion of a complex refractive index is investigated and proposed as a way to analyze the change of the optical properties of gasochromic material under the influence of diluted hydrogen (3.5% H 2 in Ar) as an active volatile medium. Therefore, a tungsten trioxide thin film and an additional platinum catalyst were deposited by electron beam evaporation and used as a prototype material. Based on experimental verification, it is shown that the proposed method allows one to explain the reasons for the observed changes in the transparency in such materials.