Time-resolved vSFG of the Water-air Interface in an External Field

In the present work we have studied the effect of an external electric field of strength ± 0.01 V/˚A on the water molecules at the water-air interface using ab-initio molecular dynam- ics. We calculated the vibrational sum-frequency generation spectra using surface-specific velocity-velocity correlation functions and used it to interpret the preferential orientation of interfacial water molecules in the presence of field. Further, we use the time-averaged fre- quency distribution and frequency correlation functions to calculate the rate of vibrational correlation loss. The rate at which hydrogen bonds under breaking and reformation at inter- face and in the presence of field is explored using time-dependent vibrational sum-frequency generation spectroscopy. We find that OH modes show faster rate of frequency correlation loss with a timescale of 4.7 ps at the presence of an external field, as compared to 5.7 ps under ambient conditions.