The problem of stability of a molecular solid with local, randomly distributed perturbations of a chemical type (substitutional, reaction generated, ionized, excited molecules) has been addressed. It has been shown that local displacement fields (lsquo;lsquo;chemical pressurersquo;rsquo;) produced by the perturbations influence stability of the solid in two ways. First, via indirect interactions between perturbations which are mediated by phonons of the host lattice and then, via modified (chemical pressure dependent) static single molecule susceptibility. The theory takes into account direct interaction between (the energy of) perturbations. A competition with indirect interaction leads to formulation of metastability as well as stability conditions. Finally, it has been shown how the conditions can be applied to predict photohyphen;induced structural changes and transformations in mixed chargendash;transfer crystals.
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