Correlation energies for AHnmolecules and cations

Correlation energies for most of the molecules and cations AH n (A = C, N, O and F) are determined by (1) obtaining estimates of the Hartree-Fock limiting energies by computation and (2) finding full non-relativistic energies for fixed nuclei by correcting experimental energies for relativistic and nuclear motion effects. It is concluded that formation of non-polar bonds to hydrogen leads to an increase in the correlation energy magnitude of just over 0·04 hartree, provided that the number of unpaired electrons is reduced. For polar bonds (NH, OH and FH) larger increases are found. If the number of unpaired electrons is not decreased by bond formation, the increase in correlation energy magnitude is smaller. It is also found that protonation of neutral species generally leads to a small decrease in correlation energy magnitudes, provided that no change in multiplicity is involved.