UC Berkeley

Broadband deep ultraviolet electronic sum frequency generation spectroscopy allows measurement of electronic |χ(2)|2-spectra at aqueous interfaces, providing considerable improvement over deep ultraviolet electronic second harmonic generation spectroscopy that yields error-prone, pointwise spectra. Reexamination of the π → π* transition of nitrite at the air/water interface reveals that the interfacial |χ(2)|2-spectrum is strikingly similar to the bulk absorption spectrum. Molecular dynamics simulations and SOS-CIS(D0) electronic structure calculations provide no evidence for the previously reported contact ion pair-induced red-shift of the π → π* transition at the air/water interface. Our results thus revise the previous description for nitrite interfacial adsorption as a contact ion pair.