AB-INITIO INVESTIGATIONS OF THE ELECTRONIC-STRUCTURE OF HENH+ AND HENH2+

Electronic structures of HeNH+ and HeNH2+ were investigated using the all-electron coupled cluster single, double and triple excitation (CCS D(T)_AE) method coupled with an augmented correlation-consistent polar ised core valence triple zeta basis set (aug-cc-pCVTZ). For HeNH+ and HeNH2+, the CCSD(T)_AE/aug-cc-pCVTZ model yielded cations of C-s symme try with (2)A '' and (1)A' ground electronic states possessing optimis ed geometrical parameters {r(N-H), r(N-He), theta(H-N-He)} of {1.064 A ngstrom, 1.517 Angstrom, 88.5 degrees} and {1.192 Angstrom, 1.309 Angs trom, 96.2 degrees} respectively. Of all the linear isomeric forms pos sible for these two cations, the only converged minimum energy structu res were for the (4) Sigma(-) states of HeHN+ and HeNH+ yielding optim ised structural parameters of {1.093 Angstrom, 2.403 Angstrom, 180.0 d egrees} and {1.117 Angstrom, 1.364 Angstrom, 180.0 degrees} respective ly. These two linear structures were calculated to be 9.6 and 18.6 kJ mol(-1) respectively above the C-s structure. The calculated harmonic frequencies were real for all these states and their magnitudes were s ensitive to the incorporation of electron correlation.