Ab initio study of XH2+ (X = B, Al, and Ga) isomers

Ab initio calculations at the MP2/6-311++G(3df.2pd) and CCSD(T)/cc-pVTZ lev els were carried out to calculate the structure and energetics of isomers o f singlet XH2+ (X = B, Al and Ga). Energy comparison shows that although th e linear D-infinity h structure 1a is the global minimum for BH2+, the glob al minima of AlH2+ and GaH2+ are not of D-infinity h symmetry 2a and 3a. re spectively, but of C-2v symmetry 2b and 3b with a 3c-2e bond. The D-infinit y h symmetric 2a and 3a are significantly less stable than 2b and 3b, respe ctively, by 13.1 and 21.5 kcal/mol. Relative hydride affinities of the cati ons 1a, 2b, and 3b were also calculated.