A DETERMINATION OF MG+-LIGAND BINDING-ENERGIES

Theoretical calculations employing large basis sets and including correlation are carried out for Mg+ with methanol, water, and formaldehyde. For Mg+ with ethanol and acetaldehyde the trends in the binding energies are studied at the self-consistent-field level. Our predictions for the binding energy of Mg+ to methanol and water of 41 +/- 5 and 36 +/- 5 kcal/mol, respectively, are much less than the experimental upper bounds, of 61 +/- 5 and 60 +/- 5 kcal/mol, determined by using photodissociation techniques. The theoretical results are inconsistent with the onset of Mg+ production observed in the photodissociation experiments, as the smallest absorptions are calculated at about 80 kcal/mol for both Mg+-CH3OH and Mg+-H2O, and these transitions are to bound excited states. The binding energy for Mg+ with formaldehyde is predicted to be similar to Mg+-H2O. The relative binding energies are in reasonable agreement with experiment. The binding energy of a second water molecule to Mg+ is predicted to be similar to the first. This suggests that the reduced reaction rate observed for the second ligand is not a consequence of a significantly smaller binding energy, at least for the smaller ligands such as those considered in this work.