Isotope effects in trapping-mediated chemisorption of ethane and propane on Ir(110)
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106 (United States)
We compare here recent results of molecular beam investigations of the initial probability of trapping-mediated C{endash}H and C{endash}D bond cleavage of C{sub 2}H{sub 6}, C{sub 2}D{sub 6}, C{sub 3}H{sub 8}, and C{sub 3}D{sub 8} on Ir(110) at low beam translational energy and surface temperatures, {ital T}{sub {ital S}}, from 85 to 800 K. Each of these systems is highly reactive at low {ital T}{sub {ital S}} and displays decreasing reactivity with increasing {ital T}{sub {ital S}}. Measurements of the initial probability of trapping-mediated chemisorption for both ethane and propane reveal an isotope effect, which we attribute to zero-point energy differences, with the perhydrido-species exhibiting greater reactivity at a given {ital T}{sub {ital S}}. A difference in activation energies for desorption vs reaction (C{endash}D bond cleavage) for C{sub 2}D{sub 6} has been found to be {ital E}{sub {ital d}}{endash}{ital E}{sub {ital r}}=1.8{plus_minus}0.3 kcal/mol, cf. {ital E}{sub {ital d}}{endash}{ital E}{sub {ital r}}=2.2 kcal/mol for C{endash}H bond cleavage of C{sub 2}H{sub 6}. For the trapping-mediated dissociative chemisorption of propane on Ir(110), {ital E}{sub {ital d}}{endash}{ital E}{sub {ital r}}=4.2 kcal/mol for C{endash}H bond cleavage of C{sub 3}H{sub 8}, and {ital E}{sub {ital d}}{endash}{ital E}{sub {ital r}}=3.2 kcal/mol for C{endash}D bond cleavage of C{sub 3}D{sub 8}. A quantitative analysis of the initial probability of trapping-mediated dissociative chemisorption of ethane and propane on Ir(110), within the context of a classical kinetic model of barrier crossing from the physically adsorbed state to the dissociatively chemisorbed state, provides the most reasonable description of the observed adsorption behavior. {copyright} {ital 1996 American Institute of Physics.}
- DOE Contract Number:
- FG03-89ER14048
- OSTI ID:
- 286920
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 9 Vol. 105; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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