Is the elusive trioxydehydroethene neutral (O₂C-CO) detectable in the gas phase?

Abstract

The covalently bound radical anion [O2C-CO]-. is formed when 1,3-dioxolane-2,5-dione captures an electron followed by retro-cleavage of CH2O. Calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory indicate that there are a number of neutral isomers with formula C2O3, viz. van der Waals complex O2C- - -CO (rel. energy = 0 kcal mol-1), singlet oxiran dione (760.9 kcal mol-1), triplet OCOCO (+99.4 kcal mol-1), covalently bound triplet O2C-CO (+ 107.6 kcal mol-1), singlet trioxapropellane (+171.9 kcal mol-1) and triplet trioxapropellane (+ 222.4 kcal mol-1). Of these, only triplet O2C-CO is accessible by vertical Franck-Condon one-electron oxidation of [O2C-CO]-.. Neutralization reionization experiments of [O2C-CO]-. (both -NR+ and -NR-) fail to produce recovery signals corresponding to ionized C2O3, which means that if neutral C2O3 is stable, the lifetime must be <10-6 sec. The -NR+ spectrum of [O2C-CO]-. shows peaks corresponding to CO+., CO2+. and to [O =C = C = O]+.. The last of these species can only be formed from a decomposing C2O3+. radical cation by a process endothermic by 47 kcal mol-1 [at the CCSD-(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory]. Calculations at this same level of theory indicate that the vertical one-electron oxidation of [O2C-CO]-. to triplet O2C-CO ground state produces the neutral with essentially no excess energy. There are two dissociation pathways of this triplet neutral, (i) an endothermic process yielding 3CO + -CO2 (+ 28.9 kcal mol-1), and (ii) an exothermic process (-6.8 kcal mol-1) with a barrier of 5.4 kcal mol-1 yielding 1CO + 3CO2. A combination of experimental and theoretical data, suggests that vertical oxidation of [O2C-CO]-. produces only one neutral C2O3 isomer; a transient triplet O2C-CO neutral whose lifetime is less than 10-6 sec.