Gaussian-2 and Gaussian-3 Study of the Energetics and Structures of Cl2On and Cl2On+, n = 1−7

The structures and energetics of the dichlorine oxides, Cl{sub 2}O{sub n}, n = 1 {minus} 7, and their cations have been investigated theoretically at the Gaussian-2 (G2) and the Gaussian-3 (G3) levels of theory. The G2 and G3 heats of formation obtained for both neutral and cationic species allow the interpretation of assigned appearance energies and ionization energies reported in a recent photoionization mass spectrometric study on these chlorine oxides. The calculations predict that Cl{sub 2}O{sub 6}{sup +} dissociates spontaneously to ClO{sub 2}{sup +} and ClO{sub 4}, in agreement with the nonobservation of Cl{sub 2}O{sub 6}{sup +} in the experimental study by Ruehl et al. For systems with n {le} 4, the calculated and experimental thermochemical properties (such as heats of formation and ionization energies) are in good to excellent agreement with each other. However, this agreement deteriorates as the size of the molecular system increases or as n exceeds 4. Thus it appears that the G3 method may also suffer from an unfavorable accumulation of component small errors, as has been found for the G2 method and its variants.