title: Communication: Ultrafast vibrational dynamics of hydrogen bond network terminated at the air∕water interface: a two-dimensional heterodyne-detected vibrational sum frequency generation study.
abstract: Ultrafast vibrational dynamics of hydrogen bond network at the air∕water interface is revealed by two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) spectroscopy. Three diagonal peaks are clearly observed in the 2D HD-VSFG spectrum, which correspond to the negative and positive hydrogen-bonded OH stretch bands and the positive "free" OH stretch band in the steady-state HD-VSFG spectrum. A diagonally elongated bleaching lobe of the hydrogen-bonded OH at 0 ps indicates that it is partly inhomogeneously broadened. This diagonal elongation vanishes in a few hundred femtoseconds, implying the ultrafast spectral diffusion in the hydrogen-bonded OH band. Off-diagonal cross peaks between each OH oscillator are clearly observed instantaneously within the time resolution of 0.2 ps, suggesting that they are vibrationally coupled through anharmonicity and∕or energy transfer.
authors.affiliation: Molecular Spectroscopy Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
authors.forename: Prashant Chandra
authors.initials: PC
authors.lastname: Singh
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nihonyanagi
authors.forename: Shoichi
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Tahei
authors.initials: T
authors.lastname: Tahara