CALCULATED AND MEASURED DOUBLE-IONIZATION ENERGIES OF ACETONITRILE TOSINGLET AND TRIPLET ELECTRONIC STATES OF THE DOUBLY-CHARGED ION

Double-ionization energies of acetonitrile (methyl cyanide) to singlet and triplet electronic states of the dication were measured and calcu lated. In the experimental part of the investigation, double-electron- capture reactions of fast-moving singly charged positive ions with ace tonitrile molecules were investigated. Double-ionization energies were determined from the translational energies of the negative ions gener ated. Because of spin conservation in the reactions, triplet states of CH3CN2+ were populated when using OH+ projectile ions, and singlet st ates when using Ht projectile ions. The double-ionization energies mea sured were compared with values calculated using two different computa tional methods. Ab initio MP2/3-21G predictions of the double-ionizati on energies to the lowest singlet and triplet states agreed well with the measured values of 34.3 +/- 0.2 and 33.3 +/- 0.3 eV, respectively. Double-ionization energies to higher-lying states were calculated usi ng an ab initio Green's function method. In general, the theoretically predicted results agreed well with those measured, thus identifying t he electronic transitions which take place in the double-electron-capt ure reactions. (C) 1997 Elsevier Science B.V.