COMPARISON OF MOLECULAR-ENERGY PREDICTIONS FOR THE NEUTRAL AND IONIC (C, H-N, O N=0-4) SYSTEM BY AB-INITIO GAUSSIAN-2 AND DENSITY-FUNCTIONAL METHODS

The ionization energies (IEs), electron affinities (EAs), total atomization energies (Sigma D-0), and bond dissociation energies at 0 K (BDEs) for the neutral and ionic (C, H-n, O, n=0-4) system are calculated at the Gaussian-2 (G2), and two levels of density functional (DF) theories. On comparing the calculated values with known experimental data, both the G2 and DF theories are capable of predicting IEs and EAs quite accurately. However, the G2 theory is far more superior to the DF theories in predicting Sigma D-0 and BDEs. Both G2 and DF theoretical calculations indicate that CO- is unstable with respect to electron detachment by approximately 1.6 eV, contrary to the experimental EA(CO)=1.4 eV based on the endothermic ion-molecule reaction study by Refaey and Franklin [Intern. J. Mass Spectrom. Ion Phys. 20 (1976) 19]. The large deviation (3eV) between experimental and theoretical results suggests that the experimental EA(CO) should be re-examined.