Vibrational spectrum of water at the liquid/vapor interface.

Abstract

The infrared spectrum of water molecules at the liquid/vapor interface of pure water and the liquid/vapor interface of a water-methanol mixture is calculated using molecular dynamics. A comparison with the IR spectrum calculated for bulk water shows a significant population of free OH bonds, in qualitative agreement with a recent experiment by Du et al. Phys. Rev. Lett. 70 2313 1993. It is also demonstrated that the free OH IR signal is quenched by a moderate increase in the concentration of methanol in bulk water, which has been recently observed by Du et al. Science 264 826 1994.