title: Interpretation of the water surface vibrational sum-frequency spectrum.
abstract: We propose a novel interpretation of the water liquid-vapor interface vibrational sum-frequency (VSF) spectrum in terms of hydrogen-bonding classes. Unlike an absorption spectrum, the VSF signal can be considered as a sum of signed contributions from different hydrogen-bonded species in the sample. We show that the recently observed positive feature at low frequency, in the imaginary part of the signal, is a result of cancellation between the positive contributions from four-hydrogen-bonded molecules and negative contributions from those molecules with one or two broken hydrogen bonds. Spectral densities for each of these subgroups span the entire relevant spectral range. Three-body interactions within our newly developed E3B water simulation model prove to be critical in describing the proper balance between different hydrogen-bonded species, as (two-body) SPC/E, TIP4P, and TIP4P/2005 models fail to reproduce the positive feature. The results clarify the molecular origin of the VSF signal, and highlight the importance of many-body interactions for water in heterogeneous situations.
authors.affiliation: Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: P A
authors.initials: PA
authors.lastname: Pieniazek
authors.forename: C J
authors.initials: CJ
authors.lastname: Tainter
authors.forename: J L
authors.initials: JL
authors.lastname: Skinner
mesh_terms: D000388:Air; D003198:Computer Simulation; D006860:Hydrogen Bonding; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D013055:Spectrophotometry, Infrared / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013057:Spectrum Analysis / Q000379:methods*; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water