Experimental and theoretical study of the electronic structure of methyl chloroformate and methyl cyanoformate

The HeI photoelectron spectra of methyl chloroformate (CH3OC(O)Cl) and methyl cyanoformate (CH3OC(O)CN) in the gas phase have been obtained for the first time. A complete theoretical study involving the calculation of the ionization energies using outer valence Green’s functional (OVGF) was performed, based on the calculated and previously reported energetically favorable cis-conformer (the carbonyl group eclipses the methyl group). Calculations of cationic-radical forms were carried out in order to interpret the main characters of the first six highest occupied molecular orbitals (HOMOs). The first vertical ionization potentials are 11.36 eV for CH3OC(O)Cl and 11.65 eV for CH3OC(O)CN, each attributed to {19a′(nO(CO), nCl)}−1 and {18a′(nO(CO))}−1, respectively.