Spin-orbit ab initio investigation of the UV photoinduced bond cleavage in iodotrimethylstannane
Résumé
The photoinduced homolytic cleavage of the Sn-I bond in iodotrimethylstannane (CH3)3SnI, observed after UV irradiation, is investigated by means of spin-orbit ab initio calculations based on CASSCF (complete active space self-consistent field) and MS-CASPT2 (multi-state complete active space 2nd order perturbation theory) methods. The absorption electronic spectrum is characterized by ten low-lying 1,3A′ and 1,3A″ spin eigenstates corresponding to py(I),px(I) → σ*SnI; σSnI → σ*SnI and py(Sn), px(Sn) → σ*SnI, where σSnI and σ*SnI are the bonding and anti-bonding orbitals of the Sn-I bond along the pz axis. From the 1A′ electronic ground state and these ten spin eigenstates, 21 spin-orbit states are generated leading to various deactivation channels of (CH3)3SnI, corresponding to the formation of radicals (CH3)3Sn* and *I and to the ionic species (CH3)3Sn+ and I-. Irradiation into the upper band at 175 nm should lead to the heterolytic cleavage of the Sn-I bond to form the ionic primary products exclusively, whereas absorption into the shoulder at 250 nm induces the homolytic breaking with formation of the radical products.