Measurements of weakly bound hydrogen on Pd(111) between 5 and 80 K
The adsorption of hydrogen and deuterium onto a low-temperature surface of Pd(111) has been studied experimentally using electron-stimulated desorption (ESD) and temperature programmed desorption spectrometry (TPD). At a surface temperature T/sub S/ = 7.5 +- 1 K, exposure to D/sub 2/ leads to multilayer formation which is reflected in the desorption of deuterium ion clusters D/sup +//sub n/ by ESD (E/sub e//sub =/ = 100 eV). Cluster sizes up to n = 21 have been observed which, except for n = 2, consist exclusively of odd numbers of atoms. The temperature dependence of the ESD signal following exposure at T/sub S/ = 7.5 +- 1 K suggests that by 9.5 +- 1 K the multilayer desorbs leaving a diatomic molecular species which, in the high-coverage limit, is stable up to --20 K. Exposure to hydrogen at these low temperatures gives rise to two TPD peaks: the ..beta.. (chemisorption) peak and a new TPD peak denoted ..gamma.. (near 60 K at low coverage) which is assigned to desorption of a surface molecular hydrogen species. Mixed isotope experiments show that there is no mixing in the ..gamma.. state consistent with this assignment. With increasing exposure, the ..gamma.. peak grows in intensity and shifts rapidly towards lower temperature. TPD peak shape analysis gives a binding energy for the molecular state at low coverage of --0.020 +- 0.010 eV and a corresponding preexponential of approximately 10/sup 2/ s/sup -1/.
- Research Organization:
- Sandia National Laboratories, Livermore, California 94550
- OSTI ID:
- 6512460
- Journal Information:
- J. Vac. Sci. Technol., A; (United States), Journal Name: J. Vac. Sci. Technol., A; (United States) Vol. 5:4; ISSN JVTAD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360104* -- Metals & Alloys-- Physical Properties
ADSORPTION
BINDING ENERGY
CHEMICAL REACTIONS
CHEMISORPTION
DATA
DESORPTION
DEUTERIUM
ELEMENTS
ENERGY
EXPERIMENTAL DATA
HYDROGEN
HYDROGEN ISOTOPES
INFORMATION
ISOTOPES
LIGHT NUCLEI
LOW TEMPERATURE
METALS
NONMETALS
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
PALLADIUM
PLATINUM METALS
SEPARATION PROCESSES
SOLID CLUSTERS
SORPTION
SORPTIVE PROPERTIES
STABLE ISOTOPES
SURFACE PROPERTIES
TRANSITION ELEMENTS
ULTRALOW TEMPERATURE
VERY LOW TEMPERATURE