The dissociative chemisorption of cyclopropane 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 dissociative chemisorption of cyclopropane on Ir(110) as a function of beam translational energy, {ital E}{sub {ital i}}, from 1.5 to 48 kcal/mol, and surface temperature, {ital T}{sub {ital s}}, from 85 to 1200 K. For {ital T}{sub {ital s}}=85 K, {ital c}-C{sub 3}H{sub 6} is molecularly adsorbed on Ir(110) with a trapping probability, {xi}, of 0.97 at {ital E}{sub {ital i}}=1.5 kcal/mol and {xi}=0.90 at {ital E}{sub {ital i}}=5 kcal/mol. For {ital E}{sub {ital i}}{le}5 kcal/mol, {ital c}-C{sub 3}H{sub 6} is dissociatively adsorbed through a mechanism of trapping-mediated chemisorption, with initial probabilities of chemisorption, {ital P}{sub {ital a}}, decreasing with increasing surface temperature from the intrinsic trapping probability at {ital T}{sub {ital s}}=150 K, to {ital P}{sub {ital a}}{lt}0.05 above {ital T}{sub {ital s}}=1000 K. The activation energy for trapping-mediated chemisorption of {ital c}-C{sub 3}H{sub 6}, referenced to the bottom of the physically adsorbed well and attributed to C{endash}C bond cleavage, is 3.6{plus_minus}0.2 kcal/mol. For {ital E}{sub {ital i}}{ge}10 kcal/mol, direct dissociative chemisorption increasingly contributes to the overall measured initial probability of chemisorption of cyclopropane. The initial probability of direct dissociative chemisorption of {ital c}-C{sub 3}H{sub 6} increases approximately linearly from {ital P}{sub {ital a}}=0.1 at {ital E}{sub {ital i}}=10 kcal/mol, to {ital P}{sub {ital a}}=0.5 at {ital E}{sub {ital i}}=45 kcal/mol. No isotope effect is observed for the direct dissociative chemisorption of {ital c}-C{sub 3}D{sub 6} for beam translational energies of 17 to 48 kcal/mol, indicating that C{endash}C bond cleavage is the initial reaction coordinate for direct chemisorption of cyclopropane on Ir(110). {copyright} {ital 1996 American Institute of Physics.}
- DOE Contract Number:
- FG03-89ER14048
- OSTI ID:
- 385651
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 16 Vol. 105; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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