Sum frequency generation vibrational spectroscopy (SFG) and cyclic voltammetry (CV) measurements have been conducted on the ionic liquid/platinum electrode system. The room-temperature ionic liquid investigated is 1-butyl-3-methylimidazolium [BMIM]+ with [PF6]- or [BF4]- anions. SFG spectra are taken in situ under potential control from 2750 to 3300 cm-1 (C−H stretching region). Polarization-dependent SFG spectra are used to extract orientation information for the cation at the electrode surface. The SFG spectra indicate that the cation changes orientation as the electrode potential is changed within the double-layer region. The plane of the imidazolium ring tips from 35° at positive surface charge to ∼60° from the surface normal at negative surface charge. Further, the orientation change is different for [BMIM][PF6] than for [BMIM][BF4]. A model for ions at the surface is presented based on these spectroscopic and electrochemical measurements.

The behavior of a water molecule in Na 6 [AlSiO 4 ] 6 sodalite has been investigated using density functional calculations. The lowest energy position of the molecule is near the plane of the 6-ring window which does not contain a Na ion. The molecule is oriented to form hydrogen bonds with two of the framework oxygens and to interact with a Na ion in a nearby window. In this configuration the energy is 0.58 eV below the energy of the isolated water molecule plus that of anhydrous sodalite. Several tests indicate that most of the binding energy is due to the interaction of the oxygen with the Na ion. An analysis of electronic density for the lowest energy position shows that, when the molecule is put in contact with sodalite, charge is transferred from the water molecule to the spaces between the hydrogen atoms and the framework oxygens and between the water molecule oxygen and the nearest Na framework ion. Other bonding sites are above the plane of a 6-ring window occupied by a Na ion and above a 4-ring window. † Part of the special issue "John T. Yates, Jr., Festschrift".