Bend Vibration of Surface Water Investigated by Heterodyne-Detected Sum Frequency Generation and Theoretical Study: Dominant Role of Quadrupole.
Heterodyne-detected vibrational sum frequency generation spectroscopy was applied to the water surface for measuring the imaginary part of second-order nonlinear susceptibility (Im χ((2))) spectrum in the bend frequency region for the first time. The observed Im χ((2)) spectrum shows an overall positive band around 1650 cm(-1), contradicting former theoretical predictions. We further found that the Im χ((2)) spectrum of NaI aqueous solution exhibits an even larger positive band, which is apparently contrary to the flip-flop orientation of surface water. These unexpected observations are elucidated by calculating quadrupole contributions beyond the conventional dipole approximation. It is indicated that the Im χ((2)) spectrum in the bend region has a large quadrupole contribution from the bulk water.
Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Achintya
A
Kundu
Department of Chemistry, Graduate School of Science, Tohoku University , Sendai 980-8578, Japan.
Shogo
S
Tanaka
Department of Chemistry, Graduate School of Science, Tohoku University , Sendai 980-8578, Japan.
Tatsuya
T
Ishiyama
Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Mohammed
M
Ahmed
Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Ken-Ichi
K
Inoue
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
Department of Chemistry, Graduate School of Science, Tohoku University , Sendai 980-8578, Japan.
Hiromi
H
Sawai
Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Shoichi
S
Yamaguchi
Department of Chemistry, Graduate School of Science, Tohoku University , Sendai 980-8578, Japan.|Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University , Kyoto 615-8520, Japan.
Akihiro
A
Morita
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