Journal article

Alignment dependent chemisorption of vibrationally excited CH4(3) on Ni(100), Ni(110), and Ni(111)

We present a stereodynamics study of the dissociative chemisorption of vibrationally excited methane on the (100), (110), and (111) planes of a nickel single crystal surface. Using linearly polarized infrared excitation of the antisymmetric C–H stretch normal mode vibration (ν 3 ), we aligned the angular momentum and C–H stretch amplitude of CH4 (ν 3 ) in the laboratory frame and measured the alignment dependence of state-resolved reactivity of CH4 for the ν3 = 1, J = 0–3 quantum states over a range of incident translational energies. For all three surfaces studied, in-plane alignment of the C–H stretch results in the highest dissociation probability and alignment along the surface normal in the lowest reactivity. The largest alignment contrast between the maximum and minimum reactivity is observed for Ni(110), which has its surface atoms arranged in close-packed rows separated by one layer deep troughs. For Ni(110), we also probed for alignment effects relative to the direction of the Ni rows. In-plane C–H stretch alignment perpendicular to the surface rows results in higher reactivity than parallel to the surface rows. The alignment effects on Ni(110) and Ni(100) are independent of incident translational energy between 10 and 50 kJ/mol. Quantum state-resolved reaction probabilities are reported for CH4 (ν 3 ) on Ni(110) for translational energies between 10 and 50 kJ/mol.

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