On the mechanism of mechanochemical dimerization of anthracene. Quantum-chemical calculation of the electronic structure of anthracene and its dimer

The electronic structure of anthracene, its dimer, and intermediate structures composed of two anthracene molecules were calculated in the density functional theory. The calculated potential barrier to anthracene dimerization is similar to 55 kcal/mol; the dissociation barrier is similar to 45 kcal/mol. The pressure required for the reaction to reach the transition state and acting on the anthracene crystal is similar to 60 kbar. Lower pressures, similar to 10 kbar, are required for molecules to approach each other to distances of similar to 3 angstrom, at which tunnel dimerization is possible for photoexcited molecules.