Experimental data of mass spectrometric analysis of vitreous As₂(S, Se)₃ chalcogenide glasses shows the perceptible difference in the values of As_m(S, Se)_n ion currents before and after laser illumination. Data of the computational calculation of the stableness of molecular units are in good correlation with obtained experimental mass spectrometric data. After laser illumination we detect new kinds of molecular units as As_m, S_n and Se_n. The observed changes of the ion currents in the mass spectrum may be explained in view of some re-arrangement in the shot-range order of the component atoms under illumination. We propose for discussion the results of computational modeling of molecular units such as As_m(S, Se)_n observed experimentally in the As₂(S, Se)₃Sn_0.1 alloys by their mass spectrometric analysis before and after laser illumination. In this report we suppose that a study of the composition of condensed molecules by the intermediacy of mass spectrometry and HyperChem Computational Chemistry Program may harvest complementary information useful in orders to building structural models of chalcogenide glasses. In result of this work we also conclude that tin atoms in the As₂(S, Se)₃Sn_0.1 network are bonded in two mode: before illumination as 2(S,Se) = Sn = 2(S,Se)-type and after illumination as (S,Se)-Sn-(S,Se)-type.