An ab initio study of the structures and properties of the XH42+ and XH62+(X = C, Si, Ge) dications

The ab initio electronic structure calculations at the MP2 and the Becke 3L YP density functional levels in conjunction with the 6-311++G(2df,2pd) basi s set were used for the determination of the structure, vibrational spectra , and dissociation energies of the XH42+ and XH62+ (X = C, Si, Ge) dication s. The minimum-energy structures correspond to the C-2v point-group symmetr y species for all studied systems and represent weakly bounded complexes of one or two H-2 molecules bounded by three-center two-electron bonds to the XH22+ core. At the DET level, we have predicted dissociation energies of 1 03.70, 88.65, 35.23, 31.97, 28.30, and 25.91 kcal/mol for CH42+ SiH42+, GeH 42+, CH62+, SiH62+, and GeH62+, respectively. Frequency shifts of the stret ching vibrations associated with the formation of weak bonds between XHn2core units and the H-2 molecules were also calculated and reported to guide experimental detections of the title species. (C) 1999 John Wiley & Sons, Inc.