| AVS 54th International Symposium | |
| Surface Science | Thursday Sessions |
| Session SS1-ThA |
| Session: | Environmental Surfaces |
| Presenter: | M.A. Brown, University of California, Irvine |
| Authors: | M.A. Brown, University of California, Irvine B. Winter, Max-Born-Institut fur Nichtlineare Optik und Kurzzeitspektroskopie, Germany M. Faubel, Max-Planck-Institut fur Dynamik und Selbstorganisation, Germany J.C. Hemminger, University of California, Irvine |
| Correspondent: | Click to Email |
The understanding of molecular arrangements and interactions at the aqueous-vapor interface is important in many chemical and biological systems where the pH dependent chemistry may vary greatly from that of the bulk. We examine the surfactant properties of hexylamine (C6H13NH2) and the protonated hexylamine ion (C6H13NH3+) at the aqueous-vapor interface. The state of this acid/base equilibrium couple should shed light on the local pH of the aqueous interface, as well as the relative aqueous solvation of the two species. Chemical shifts are observed in the N (1s) and C (1s) photoemission spectra due to protonation of the amine, allowing us to clearly identify and quantify the two species. The experiments use a 15 µm liquid micro-jet free vacuum surface at a micro-focus x-ray beamline of the BESSY synchrotron radiation facility. The bulk pH of solution is varied by addition of HCl in order to vary the degree of hexylamine protonation. Varying the energy of the ejected photoelectrons by carrying out experiments as a function of x-ray wavelength allows us to generate a depth profile of the aqueous-vapor interface. The core level O (1s), N (1s) and C (1s) photoemission spectra were collected as a function of photoelectron kinetic energy, creating a molecular level picture of the entire interfacial region. Results show that the concentration of hexylamine (C6H13NH2) is greatly enhanced at the interface relative to the protonated hexylamine ion (C6H13NH3+). Peak broadening, and relative peak intensities vary with bulk pH, and are attributed to changes in molecular packing.