Abstract
The reactivity of methane (CH 4 ) on Pt(110)-(1×2) Pt(110)-(1×2) has been studied by quantum state-resolved surface reactivity measurements. Ground state reaction probabilities, S 0 (v=0)≅S 0 (laser-off) S0(v=0)≅S0(laser-off) , as well as state-resolved reaction probabilities S 0 (2ν 3 ) S0(2ν3) , for CH 4 CH4 excited to the first overtone of the antisymmetric C–H stretch (2ν 3 ) (2ν3) have been measured at incident translational energies in the range of 4–64 kJ/mol. We observe S 0 (2ν 3 ) S0(2ν3) to be up to three orders of magnitude higher than S 0 (v=0) S0(v=0) , demonstrating significant vibrational activation of CH 4 CH4 dissociation on Pt(110)-(1×2) Pt(110)-(1×2) by 2ν 3 2ν3 excitation. Furthermore, we explored the azimuthal and polar incident angle dependence of S 0 (2ν 3 ) S0(2ν3) and S 0 (v=0) S0(v=0) for a fixed incident translational energy E t =32 kJ/mol Et=32 kJ/mol . For incidence perpendicular to the missing row direction on Pt(110)-(1×2) Pt(110)-(1×2) and polar angles θ>40° θ>40° , shadowing effects prevent the incident CH 4 CH4 molecules from impinging into the trough sites. Comparison of this polar angle dependence with reactivity data for incidence parallel to the missing rows yields state-resolved site specific reactivity information consistent with a Pt(110)-(1×2) Pt(110)-(1×2) reactivity that is dominated by top layer Pt atoms located at the ridge sites. A comparison of S 0 (v=0) S0(v=0) measured on Pt(110)-(1×2) Pt(110)-(1×2) and Pt(111) yields a lower average barrier for Pt(110)-(1×2) Pt(110)-(1×2) by 13.7±2.0 kJ/mol 13.7±2.0 kJ/mol .