Quantum chemical calculations of electronically excited states: formamide, its protonated form and alkali cation complexes as case studies

The properties of formamide, its protonated form and interaction complexes with lithium and sodium cations were studied in electronically excited singlet states by means of high-level multireference ab initio methods. The vertical excitation energies show a marked influence on protonation with particular large effects found for the O-protonated form as compared to neutral formamide. Complexation with Li⁺ and Na⁺ leads to a pronounced shift of the n_O–π^* state to higher energies while the π–π^* state moves in opposite direction. Geometry optimizations in the lowest excited singlet show strong geometrical effects leading to pyramidalization at the N and C atoms. The photodynamical simulations performed for formamide in the first excited singlet state show that the main primary deactivation path is CN dissociation with a lifetime of about 420?fs.