J. Phys. Chem. C 2008, 112, 8359–8364
8359
Photoionization of Sodium Salt Solutions in a Liquid Jet G. A. Grieves,† N. Petrik,‡ J. Herring-Captain,† B. Olanrewaju,† A. Aleksandrov,† R. G. Tonkyn,‡ S. A. Barlow,‡ G. A. Kimmel,‡ and T. M. Orlando*,† School of Chemistry and Biochemistry, Georgia Institute of Technology Atlanta, Georgia 30332-0400, and Fundamental Sciences Directorate, Pacific Northwest National Laboratory, Mail Stop K8-88, P.O. Box 999, Richland, Washington 99352 ReceiVed: October 23, 2007; ReVised Manuscript ReceiVed: February 26, 2008
A liquid microjet was employed to examine the gas/liquid interface of aqueous sodium halide (Na+X-, X ) Cl, Br, I) salt solutions. Laser excitation at 193 nm produced and removed cations of the form H+(H2O)n and Na+(H2O)m from liquid jet surfaces containing either NaCl, NaBr or NaI. The protonated water cluster yield varied inversely with increasing salt concentration, while the solvated sodium ion cluster yield varied by anion type. The distribution of H+(H2O)n at low salt concentration is identical to that observed from lowenergy electron irradiated amorphous ice, and the production of these clusters can be accounted for using a localized ionization/Coulomb expulsion model. Production of Na+(H2O)m is not quantitatively accounted for by this model but requires ionization of solvation shell waters and a contact ion/Coulomb expulsion mechanism. The reduced yields of Na+(H2O)m from high concentration (10-2 and 10-1 M) NaBr and NaI solutions indicate a propensity for Br- and I- at the solution surfaces and interfaces. This is supported by the observation of multiphoton induced production and desorption of Br+ and I+ from the 10-2 and 10-1 M solution surfaces. Introduction Heterogeneous gas interfaces are important in a wide variety of fields such as atmospheric chemistry, astrochemistry and biochemistry.1–6 Atmospheric ice particles and droplets provide crucial platforms for reactions. Several of these reactions involving ice particles and liquid aerosol droplets in polar stratospheric cloud (PSCs) have implications for ozone destruction.1,3 Despite their importance, these interfaces are not well understood due to experimental limitations. Some studies have used low temperature amorphous ice as a surrogate for liquid water in atmospherically relevant interactions.7,8 While these studies utilize surface sensitive methods to examine reactions, the necessity for ultrahigh vacuum conditions limits the temperature to
