Unveiling the Janus-Like Properties of OH(-)

Using ab initio simulations, we explore the glassy landscape of the OH(-)(H2O)20 cluster and its infrared spectrum. We show that the OH(-) has an amphiphilic Janus-type behavior like the hydronium ion induced by the ability of its O-H bond to be buried inside of the cluster or exposed at the surface with different coordination numbers. Recent infrared experiments of aqueous NaOH have found two pronounced peaks at 2000 and 2850 cm(-1) [Mandal, A.; J. Chem. Phys. 2014, 140, 1-12]. The microscopic origins of these spectral features remain elusive. Herein, we disentangle the contribution of the spectra between 1700 and 3000 cm(-1) in terms of the microscopic solvation structure of OH(-) and dub this as the amphiphilic band. The delocalized nature of OH(-) results in a red shift to the O-H stretch, which mixes with bend-vibrations, the extent to which is tuned by the local coordination number. These results have important bearing on understanding the spectroscopic signatures of OH(-) in environments like the air-water interface.