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Electronic excitation of Solid Rare Gases induces substantial lattice distortions. One of these is the formation of an excited state dimer $R2\ast$ in a regular lattice. The data have been obtained which suggest that the self-trapping into molecular states results in a production of $defects1$. In this paper we present recent results on creation and modification of structural defects during formation of molecular centers $R2\ast$ and after their dissociation. The experiments were performed under low temperature irradiation by an electron beam of subthreshold energy. The defects were detected by means of vacuum ultraviolet luminescence spectroscopy. Dose dependencies of emission spectra of $R2\ast$ were studied in a temperature range where the thermal fluctuation processes of defect formation and diffusion were ``frozen out''. A build-up of stable point defects in samples was found. Based upon the analysis of the temperature and dose dependencies we have proposed two mechanisms of defect formation induced by trapping into dimer states: excited state molecule mechanism and ground-state molecular one. It is assumed that the off-center displacement of excted state dimers gives rise to an irreversible lattice distortion prior to radiative decay. The local distortions persist in the form of structural defects after annihilation of electronic excitations. It is shown that the defect formation processes occure in long-lived electronic state $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma u+$.