An experimental and computational study of the double ionization of CH3Cl,CH2Cl2, and CHCl3 molecules to singlet and triplet electronic states of their dications

Experimental and computational methods were applied to study the double ion ization of the molecules CH3Cl, CH2Cl2, and CHCl3. Double-charge-transfer s pectroscopy was applied to measure the double-ionization energies of the mo lecules. The translational energies of the negative ions generated when fas t-moving singly charged positive projectile ions acquire two electrons in c ollisions with the molecules provides information on the states of the dica tions populated. The use of H+, OH+, and F+ projectile ions allowed transit ions to singlet and triplet electronic states of the dications to be studie d. Double-ionization energies to those states were calculated using the sec ond order algebraic diagrammatic construction Green's function method. The calculated and measured values for CH3Cl were found to be in good agreement . The computed data predicted that the density of states for CH2Cl22+ and C HCl32+ were much higher than for CH3Cl2+. On grouping the calculated double -ionization energies to close-lying states together, however, good agreemen t with the measured values was evident. The combined experimental and compu tational study reported here thus provides a detailed understanding of the double ionization of the three molecules to singlet and triplet electronic states of their dications. (C) 1999 Elsevier Science B.V.