2D heterodyne-detected sum frequency generation study on the ultrafast vibrational dynamics of H{sub 2}O and HOD water at charged interfaces

• Published in: The Journal of chemical physics 2015-06, Vol.142 (21)
• Main Authors: Inoue, Ken-ichi, Singh, Prashant C., Nihonyanagi, Satoshi, Tahara, Tahei, Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics, 2-1 Hirosawa, Wako, Saitama 351-0198, Yamaguchi, Shoichi, Department of Applied Chemistry, Saitama University, 255 Shimo-Okubo, Saitama 338-8570
• Format: Article
• Language: English
• Subjects: ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; AMMONIUM COMPOUNDS; BLEACHING; BROMIDES; CHEMICAL BONDS; DIFFUSION; EXCITATION; FERMI RESONANCE; FREQUENCY DEPENDENCE; HEAVY WATER; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; INTERFACES; STEADY-STATE CONDITIONS; TIME RESOLUTION; TWO-DIMENSIONAL CALCULATIONS; TWO-DIMENSIONAL SYSTEMS
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4918644

Two-dimensional heterodyne-detected vibrational sum-frequency generation (2D HD-VSFG) spectroscopy is applied to study the ultrafast vibrational dynamics of water at positively charged aqueous interfaces, and 2D HD-VSFG spectra of cetyltrimethylammonium bromide (CTAB)/water interfaces in the whole hydrogen-bonded OH stretch region (3000 cm{sup −1} ≤ ω{sub pump} ≤ 3600 cm{sup −1}) are measured. 2D HD-VSFG spectrum of the CTAB/isotopically diluted water (HOD-D{sub 2}O) interface exhibits a diagonally elongated bleaching lobe immediately after excitation, which becomes round with a time constant of ∼0.3 ps due to spectral diffusion. In contrast, 2D HD-VSFG spectrum of the CTAB/H{sub 2}O interface at 0.0 ps clearly shows two diagonal peaks and their cross peaks in the bleaching region, corresponding to the double peaks observed at 3230 cm{sup −1} and 3420 cm{sup −1} in the steady-state HD-VSFG spectrum. Horizontal slices of the 2D spectrum show that the relative intensity of the two peaks of the bleaching at the CTAB/H{sub 2}O interface gradually change with the change of the pump frequency. We simulate the pump-frequency dependence of the bleaching feature using a model that takes account of the Fermi resonance and inhomogeneity of the OH stretch vibration, and the simulated spectra reproduce the essential features of the 2D HD-VSFG spectra of the CTAB/H{sub 2}O interface. The present study demonstrates that heterodyne detection of the time-resolved VSFG is critically important for studying the ultrafast dynamics of water interfaces and for unveiling the underlying mechanism.