Partially Hydrated Electrons at the Air/Water Interface Observed by UV-Excited Time-Resolved Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy.
Hydrated electrons are the most fundamental anion species, consisting only of electrons and surrounding water molecules. Although hydrated electrons have been extensively studied in the bulk aqueous solutions, even their existence is still controversial at the water surface. Here, we report the observation and characterization of hydrated electrons at the air/water interface using new time-resolved interface-selective nonlinear vibrational spectroscopy. With the generation of electrons at the air/water interface by ultraviolet photoirradiation, we observed the appearance of a strong transient band in the OH stretch region by heterodyne-detected vibrational sum-frequency generation. Through the comparison with the time-resolved spectra at the air/indole solution interface, the transient band was assigned to the vibration of water molecules that solvate electrons at the interface. The analysis of the frequency and decay of the observed transient band indicated that the electrons are only partially hydrated at the water surface, and that they escape into the bulk within 100 ps.
Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.|Department of Chemistry, School of Science, The University of Tokyo , 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Korenobu
K
Matsuzaki
Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Ryoji
R
Kusaka
Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.|Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Satoshi
S
Nihonyanagi
Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.|Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Shoichi
S
Yamaguchi
Department of Chemistry, School of Science, The University of Tokyo , 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Takashi
T
Nagata
Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.|Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Tahei
T
Tahara