Probing photochemical dynamics using electronic vs vibrational sum-frequency spectroscopy: The case of the hydrated electron at the water/air interface

Photo-dynamics can proceed differently at the water/air interface compared to in the respective bulk phases. Second-order non-linear spectroscopy is capable of selectively probing the dynamics of species in such an environment. However, certain conclusions drawn from vibrational and electronic sum-frequency generation spectroscopies do not agree as is the case for the formation and structure of hydrated electrons at the interface. This Perspective aims to highlight these apparent discrepancies, how they can be reconciled, suggests how the two techniques complement one another, and outline the value of performing both techniques on the same system.