Spectroscopy, structure and energy flow for acetylene on sodium chloride
Polarized IR absorption spectra of C[sub 2]H[sub 2] and C[sub 2]D[sub 2] on NaCl(100) provide information about the adlayer structure. At saturated coverage the [nu][sub 3] band of acetylene is split into three peaks. Multiple peaks for this nondegenerate vibration result from both correlation-field and static-field splittings. The spectra are qualitatively explained by an ordered bilayer structure similar to 1.5 layers of the low-temperature crystalline structure of acetylene. The authors also find evidence for a high-temperature, disordered, lattice-gas phase of this system. Upon exposure to 184.9 nm light the lattice gas undergoes a hydrogen exchange reaction, while the ordered phase is unreactive. In contrast to gas-phase photolysis, which yields a polymer, molecular hydrogen and collection of small hydrocarbons, no products other than acetylene isotopomers are observed in the surface reaction. The rate of the reaction shows an exponential temperature dependence and is interpreted as being surface diffusion limited. The authors propose that this photochemical hydrogen exchange occurs by a radical chain mechanism. UV luminescence spectra from a thin, polycrystalline film of NaCl are also presented. This luminescence results from the radiative recombination of the electron and hole of the self trapped exciton (STE) of NaCl. Upon adsorption of a monolayer of acetylene, luminescence from the excited triplet state of the STE is quenched. The authors propose that this quenching is due to triplet-triplet energy transfer between the STE of NaCl and the T[sub 1] state of adsorbed acetylene molecules.
- Research Organization:
- Indiana Univ. Foundation, Bloomington, IN (United States)
- OSTI ID:
- 6959025
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTRA
ACETYLENE
ADSORPTION
ALKALI METAL COMPOUNDS
ALKYNES
CHLORIDES
CHLORINE COMPOUNDS
DEUTERIUM COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HYDROCARBONS
HYDROGEN COMPOUNDS
ORGANIC COMPOUNDS
SODIUM CHLORIDES
SODIUM COMPOUNDS
SORPTION
SORPTIVE PROPERTIES
SPECTRA
SURFACE PROPERTIES