Structure, energetics, and vibrational spectrum of ammonia...water

The geometry of H3N-HOH is fully optimized by using a number of basis sets including 6-31G** and variants which add a second set of d-functions and a diffuse sp-shell. The internal geometries are altered very little as a result of complexation with the exception of a 0.008-A stretch of the bridging N-H bond; N-H-0 is within 5 O of linearity. The electronic binding energy of the complex is 5.7 kcal/mol, 1.2 kcal/mol of which is a result of electron correlation. The calculations confirmthe expected red shift and intensification of the v, band of the proton donor molecule within the complex. All of the intermolecular modes are calculated and used to help assign bands in the experimental spectrum.