Direct dissociative chemisorption of propane on Ir(110)
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106 (United States)
We have employed molecular beam techniques to investigate the initial probability of direct dissociative chemisorption, {ital P}{sub {ital d}}, and the intrinsic trapping probability, {xi}, of C{sub 3}H{sub 8}, C{sub 3}D{sub 8}, and (CH{sub 3}){sub 2}CD{sub 2} on Ir(110) as a function of beam translational energy, {ital E}{sub {ital i}}, from 1.5 to 59 kcal/mol. For C{sub 3}H{sub 8} and (CH{sub 3}){sub 2}CD{sub 2}, a measurable ({ge}0.02) initial probability of direct dissociative chemisorption is observed above a beam energy of approximately 7 kcal/mol. For C{sub 3}D{sub 8} this energy is roughly 10 kcal/mol. Above these energies the initial probability of direct chemisorption of each of the isotopomers of propane increases nearly linearly with {ital E}{sub {ital i}}, approaching a value of approximately {ital P}{sub {ital d}}=0.48 at {ital E}{sub {ital i}}=52 kcal/mol for C{sub 3}H{sub 8} and (CH{sub 3}){sub 2}CD{sub 2}, and {ital P}{sub {ital d}}=0.44 at {ital E}{sub {ital i}}=59 kcal/mol for C{sub 3}D{sub 8}. This kinetic isotope effect for the direct chemisorption of C{sub 3}D{sub 8} relative to C{sub 3}H{sub 8} is smaller than that expected for a mechanism of H (or D) abstraction by tunneling through an Eckart barrier, suggesting a contribution of C{endash}C bond cleavage to direct chemisorption. The lack of a kinetic isotope effect for the direct chemisorption of (CH{sub 3}){sub 2}CD{sub 2} relative to C{sub 3}H{sub 8} indicates that 1{degree} C{endash}H bond cleavage dominates over 2{degree} C{endash}H bond cleavage during the direct chemisorption of propane on Ir(110). The trapping behavior of each of these isotopomers of propane is approximately identical as a function of {ital E}{sub {ital i}}, with {xi}{gt}0.9 at {ital E}{sub {ital i}}=1.5 kcal/mol, {xi}=0.3 at {ital E}{sub {ital i}}=20 kcal/mol, and {xi}{lt}0.1 above {ital E}{sub {ital i}}=40 kcal/mol. {copyright} {ital 1996 American Institute of Physics.}
- DOE Contract Number:
- FG03-89ER14048
- OSTI ID:
- 402513
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 24 Vol. 105; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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