Ultrafast reorientation of dangling OH groups at the air-water interface using femtosecond vibrational spectroscopy.
We report the real-time measurement of the ultrafast reorientational motion of water molecules at the water-air interface, using femtosecond time- and polarization-resolved vibrational sum-frequency spectroscopy. Vibrational excitation of dangling OH bonds along a specific polarization axis induces a transient anisotropy that decays due to the reorientation of vibrationally excited OH groups. The reorientation of interfacial water is shown to occur on subpicosecond time scales, several times faster than in the bulk, which can be attributed to the lower degree of hydrogen bond coordination at the interface. Molecular dynamics simulations of interfacial water dynamics are in quantitative agreement with experimental observations and show that, unlike in bulk, the interfacial reorientation occurs in a largely diffusive manner.
FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
Cho-Shuen
CS
Hsieh
R Kramer
RK
Campen
Ana Celia
AC
Vila Verde
Peter
P
Bolhuis
Han-Kwang
HK
Nienhuys
Mischa
M
Bonn
D000388:Air; D006860:Hydrogen Bonding; D017665:Hydroxyl Radical / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*; D013997:Time Factors; D014732:Vibration; D014867:Water / Q000737:chemistry*
D014867:Water; D017665:Hydroxyl Radical