The Infrared Absorption Spectrum of Water

Abstract

A combination of quantum calculations and Monte Carlo methods is used to predict the infrared absorption spectrum of the water monomer, water dimer and the pure liquid. Full quantum calculations using internal coordinates are used to fit three Morse oscillators to the fundamental and overtone vibrations of the water monomer. This intramolecular potential is then combined with an accurate intermolecular surface to calculate the dimer spectrum from a normal mode analysis and from classical trajectory studies. The liquid state spectrum is obtained using a Monte Carlo simulation program together with a sequence of normal mode analyses of representative molecular configurations. Results are in good agreement with available experimental data suggesting that the potential energy surfaces used are reasonably accurate.