Schepin A.S., Peshkov S.A., Peshkova T.V.
LIFETIME SINGLET OXYGEN IN THE COLLISIONAL COMPLEX O₂-CO₂ ^{[№ 3 ' 2016]}
One of the most promising emerging in our time method to eliminate malignant tumors is photodynamic therapy. We study the mechanism that explains the increase in the lifetime of singlet oxygen in living organisms when administered by photodynamic therapy using a computer simulation. The methods of self-consistent field (SCF/ROHF) and density functional theory (DFT/B3LYP) held conformational analysis to determine the geometrical characteristics of the oxygen complexes with carbon dioxide and identify among them the most stable structure with minimum energy. Multi-configurationally method CASSCF (14, 11) designed the electronic terms of the complex ^1,3[O₂-CO₂]. The method of spin-orbit interaction (SOC) calculated moments of forbidden transitions a¹Δ_g — X³∑_g^–, b¹∑_g⁺ — a¹Δ_g, Einstein coefficients (transition probabilities), as well as the lifetime of singlet oxygen (a¹Δ_g, b¹∑_g⁺) by complexing with oxygen molecules of carbon dioxide molecule. Identify the most stable structure of the complex [O₂-CO₂] — II, having chiseled C_2v group symmetry. It was revealed that the ground and the excited state of oxygen in complex ^1,3[O₂-CO₂] O₂(X³∑_g^– + CO₂(A¹∑_g⁺), O₂(a¹Δ_g; a'¹Δ'_g) + CO₂(A¹∑_g⁺), O₂(b¹∑_g⁺) + CO₂(A¹∑_g⁺) are low stability, as they have low energy dissociation. The possibility of manifestation forbidden transitions induced moment's a¹Δ_g — X³∑_g^–, b¹∑_g⁺ — a¹Δ_g in the O₂ molecule by the action of carbon dioxide a collision molecules that virtually do not appear in a separate O₂ molecule. The calculated value of the lifetime of singlet oxygen in collision complexes ^1,3[O₂-CO₂] describes the possibility of the formation of complexes of oxygen with carbon dioxide, and other low molecular weight compounds having a membrane transport in the tissues of a living organism in their low-intensity laser irradiation, whereby, increases the lifetime of singlet oxygen O₂(a¹Δ_g, b¹∑_g⁺).