Hydrogen bonding and the protonated water dimer

A semi-empirical AM1 study of hydrogen bonding and protonation in water has been carried out to illustrate the two different O-H vibrational Frequenci es present in the protonated water dimer, H5O2+. Using the MOPAC quantum me chanical program, it is shown that the optimized geometry for this species is C-2h, With an O-H bond distance of 1.20 Angstrom, and the fifteen normal frequencies have been determined. Results predict the two O-H vibrational Frequencies at 553 and 3300 cm(-1), with the former being the H-bond stretc hing mode. A grid calculation illustrating how the potential energy surface of water varies with the H-O-H angle and the O-H bond distance is also pre sented.