Average molecular orientations in the adsorbed water layers on silicon oxide in ambient conditions

Anna L. Barnette, David B. Asay, Seong H. Kim

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47 Scopus citations

Abstract

The average molecular orientation in the adsorbed water layers formed on amorphous SiO2 in ambient conditions was determined as a function of relative humidity using polarization attenuated total reflectance infrared spectroscopy (ATR-IR). The silicon oxide surface was prepared by chemically cleaning in aqueous solution, washing with water, and drying with argon. After drying, this produced a SiO2 surface with hydroxyl groups, giving rise to a water contact angle <5°. Primarily two types of vibrational peaks that correspond to liquid water and solid-like water were observed in the adsorbed water layers formed on this surface at room temperature. The average orientation of the water molecules was determined from the dichroic ratio of s- to p-polarization absorbances. At low relative humidities, the highly hydrogen bonded solid-like structure exhibits a dichroic ratio as low as ∼0.4, while the liquid water structure exhibits a dichroic ratio close to ∼1.0. As the relative humidity increases, the dichroic ratio of both water structures approaches a dichroic ratio of 0.7∼0.8, which is consistent with the random orientation of molecules of bulk water and ice.

Original languageEnglish (US)
Pages (from-to)4981-4986
Number of pages6
JournalPhysical Chemistry Chemical Physics
Volume10
Issue number32
DOIs
StatePublished - 2008

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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