Time-dependent vibrational sum-frequency generation spectroscopy of the air-water interface

Abstract

Vibrational sum-frequency generation spectroscopy is a powerful method to study the microscopic structure and dynamics of interfacial systems. Here we demonstrate a simple computational approach to calculate the time-dependent, frequency-resolved vibrational sum-frequency generation spectrum (TD-vSFG) of the air-water interface. Using this approach, we show that at the air-water interface, the transition of water molecules with bonded OH modes to free OH modes occurs at a time scale of $3 ps, whereas water molecules with free OH modes rapidly make a transition to a hydrogen-bonded state within $2 ps. Furthermore, we also elucidate the origin of the observed differential dynamics based on the time-dependent evolution of water molecules in the different local solvent environments.

Hydrogen bond dynamics of interfacial water molecules revealed from two-dimensional vibrational sum-frequency generation spectroscopy

“…The vSFG spectrum is mathematically expressed as 5 where is the second-order susceptibility, is the transition dipole moment and is the polarizability of the system. The time-resolved vSFG spectrum 28 can be obtained from the above-mentioned equation without calculating the higher order response functions by explicitly introducing a time parameter , i.e. Here, we compute the susceptibility of a vibrational oscillator that is oscillating at vibrational frequency at time .…”

“On-The-Fly” Calculation of the Vibrational Sum-Frequency Generation Spectrum at the Air-Water Interface

“…Furthermore, it can be directly applied to spectral decomposition by computing fragment-specific contributions from the Wannier centers and their second moment to assist the interpretation of the experimental measurements. Moreover, the algorithm employed here can be easily extended to other spectroscopic techniques like two-dimensional v-SFG [ 67 ], time-dependent v-SFG [ 68 ], 2D-Raman-Thz [ 69 ], pump-probe Thz [ 70 ], and 2D-Raman [ 71 ] to name just a few. From the application perspective, interfacial reactivity, on-water catalysis, and other interfacial chemical processes can also be studied using our anisotropic WP-based method.…”

“On-the-fly” calculation of the Vibrational Sum-frequency Generation Spectrum at the Air-water Interface

“…Furthermore, it can be directly applied to spectral decomposition by computing fragment-specific contributions from the Wannier centers and their second moment to assist the interpretation of the experimental measurements. Moreover, the algorithm employed here can be easily extended to other spectroscopic techniques like two-dimensional v-SFG, [65] time-dependent v-SFG, [66] 2D-Raman-Thz, [67] pump-probe Thz [68] and 2D-Raman, [69] to name just a few. From the application perspective, interfacial reactivity, "on-water" catalysis, and other interfacial chemical processes can also be studied using our anisotropic WP-based method.…”