Absorption of Methylene, Hydrohalogenocarbenes and Dihalogenocarbenes in the Ultraviolet Visible Range: Ab Initio and Density Functional Theory (DFT) Approaches

Carbenes are unstable biradical molecules with a longer lifetime in space than on Earth. This theoretical study focused on analyzing the spectroscopic properties of methylene and monohalogenated and dihalogenated derivatives in the ultraviolet-visible range. Structures of these compounds can exist in two electronic states depending on the orbitals containing the non-bonding electrons: singlet S 0 and triplet T 1 . Three theoretical levels HF/6-311++G (d, p), MP2/6-311++G (d, p), and B3LYP/6-311++G (d, p) were used to perform this analysis. Absorption spectra were calculated for the optimized structures (S 0 and T 1 ) of methylene, three hydrohalogenocarbenes and two dihalogenocarbenes at each of the chosen theoretical levels. The calculations allowed us to study the behavior of these carbenes in ultraviolet-visible absorption. It was determined that, at maximum absorption, all of these carbenes in the singlet S 0 state absorb in the visible range. However, in the T 1 triplet state, they absorb in the ultraviolet range. Under maximum oscillation conditions, these carbenes absorb in the ultraviolet regardless of the electronic state of the structure. The calculated absorption wavelengths show that the transition from the ground state to their excited states of the studied carbenes is sometimes accompanied by a bathochromic effect and sometimes by a hypsochromic effect.