Water Bending Mode at the Water-Vapor Interface Probed by Sum-Frequency Generation Spectroscopy: A Combined Molecular Dynamics Simulation and Experimental Study.
We present a combined molecular dynamics simulation and experimental study on the water bending mode at the water-vapor interface using sum-frequency generation (SFG) spectroscopy. The SFG spectrum simulated using an ab initio-based water model shows good agreement with the experimental data. The imaginary part of the SFG response shows a negative peak at ∼1650 cm(-1) and a positive peak at ∼1730 cm(-1). Our results reveal that these widely (∼80 cm(-1)) separated peaks result from the interference of two closely spaced (∼29 cm(-1)) peaks of opposite sign. The positive peak at ∼1689 cm(-1) originates from water with two donor hydrogen atoms with the HOH angular bisector pointing down toward the bulk, and the negative peak at ∼1660 cm(-1) from water with free O-H groups, pointing up. The small frequency difference of 29 cm(-1) indicates that the HOH bending mode frequency of interfacial water is relatively insensitive to the number of hydrogen bonds.
†Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
Yuki
Y
Nagata
†Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.|‡FOM-Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands.
Cho-Shuen
CS
Hsieh
§Max-Planck Research Department for Structural Dynamics, University of Hamburg, Center for Free Electron Laser Science, Luruper Chausee 149, 22607, Hamburg, Germany.
Taisuke
T
Hasegawa
†Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
Judith
J
Voll
†Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
Ellen H G
EH
Backus
†Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
Mischa
M
Bonn
free OH group; hydrogen bonding; molecular dynamics simulation; surface-specific spectroscopy; vibrational