ABINITIO STUDY OF GEOMETRICALLY METASTABLE MULTIPROTONATED SPECIES - MHNK+

The geometries and stabilities relative to fragmentation of H4O2+, H4S2+, H3F2+, H3Cl2+, H2Ne2+, H2Ar2+, H4F3+, H4Cl3+, H3Ne3+, H3Ar3+, H4Ne4+, and H4Ar4+ have been studied using the quadratic configuration interaction (with single and double excitations plus approximate triple excitations included) QCISD (T)/6-311G(2df,2p) method at second-order Moller-Plesset optimized geometries MP2(full)/TZP+ZPE/6-31G**. All of the triply charged H4F3+, H4Cl3+, H3Ne3+, and H3Ar3+ and more highly charged H4Ne4+ and H4Ar4+ ions, as well as doubly charged H2Ne2+ were not found to possess local minima on their zero-point corrected ground state surfaces, although H4Cl3+ is only slightly unstable. Tetrahedral (T(d)) structures for H4O2+ and H4S2+, planar triangular (D3h) H3F2+, triangular pyramidal (C3v) H3Cl2+ and bent (C2v) H2Ar2+ were found to be local minima on the respective ground state surfaces. The latter five species lie above their respective ion-plus-ion dissociation products by 61, 91, 111, 67, and 116 kcal/mol, and have barriers to dissociation of 38, 20, 12, 34, and 5 kcal/mol (all energies being zero-point corrected). Such multiply charged cations store a great deal of energy, which may be released by the addition of a single extra electron to form the corresponding cation of one less charge.