Fragmentation of Protonated Dimethylaminoazobenzene during Laser Pulsed Photolysis in a Cryogenic Atmosphere of Rarefied Helium

An analysis is performed for data on the composition of cationic fragments formed during the pulsed photolysis of protonated form of dimethylaminoazobenzene dye in a rarefied helium atmosphere at T ≈ 40 K. It is shown that the interpretation of the mechanism of photolysis, which is based on the traditional representation of this dye as a monomeric azonium cation, is incorrect. An adequate mechanism of the process is obtained using a new concept, according to which the ground state of protonated dimethylaminoazobenzene and its substituted derivatives are rydimers with two protonated amino groups. It was established that the photoexcitation of these rydimers in an atmosphere of rarefied helium results their deprotonation, accompanied by the formation of electrically neutral monomers and monomers with positive charges on sp 2 orbitals. Both types of monomers react in a helium atmosphere with released protons, splitting into different cationic fragments. Formulas for the structure of fragments and schemes of monomer fragmentation are presented.