TPD NH3 HF H2O Au(111) - The influence o f a...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
The influence of adsorbate-absorbate hydrogen bonding in molecular chemisorption: NH 3 , HF, and H 2 0 on Au(111) Bruce D. Kay, Keith R. Lykke, J. Randall Creighton, and Stephen J. Ward Sandia National Laboratories, Albuquerque, New Mexico 87175 (Received 2 May 1989; accepted 30 June 1989) Hydrogen bonding plays a pervasive role in nature, be- ing important in such diverse areas as the nonideal gas be- havior and anomalous boiling points of associated vapors and liquids, the crystal structure of molecular solids, the homogeneous nucleation of atmospheric aerosols, and the binding of nucleic acid base pairs in biological systems. 1,2 Presently, surprisingly little is known about the role hydro- gen bonding plays in the molecular chemisorption of mole- cules on surfaces. In this note we report results of recent molecular beam and temperature programmed desorption (TPD) experiments which examine the adsorption-desorp- tion kinetics of three classically hydrogen bonded molecules, NH 3 , HF, and H 2 0, from a relatively chemically inert metal- lic substrate, Au ( 111 ) . Figure 1 displays representative TPD spectra for var- ious coverages ofNH 3 , HF, and H 2 0 adsorbed on Au( 111) at 85 K which are subsequently desorbed during a linear thermal ramp of2.0 K/s. The Au( 111) sample resides in an UHV surface analytical chamber (base pressure < 2 X 10- 10 Torr) and is dosed by a quadruply differentially pumped 300 K effusive molecular beam source having a flux of - 1013 molecules cm - 2 S - 1 and a cross-sectional area of -0.1 cm 2 [roughly 5% of the -1 cm diameter Au(111) sample]. This dosing source enables precise and reproduc- ible exposures to be attained without appreciable adsorption on surfaces other than the crystal target. The beam dosing technique also allows the absolute molecular sticking coeffi- cient to be directly determined by the beam reflection tech- nique of King and Wells. 3 At 85 K the molecular sticking coefficients for NH 3 , HF, and H 2 0 are always greater than 0.95 and are independent of coverage (including multi- layers) and incident angle (9;<60°) indicting the adsorp- tion kinetics are markedly non-Langmuirian. For each molecule the adsorption is molecular in na- ture, consistent with the chemically inert nature of Au ( 111 ), and in each case desorption is complete by 170 K indicating that the adsorbates are only weakly bound to the metallic substrate. Interestingly, the resultant TPD spectra are qualitatively different for the various species. The NH3
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern