Search

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

The quantum state-resolved reactivity S0 of SiH4 on Si(100)-2×1 has been measured for the first time for two vibrationally excited Si–H stretch local mode states (|2000> and |1100>) as well the ground state S0 as a function of translational energy En and surface temperature Ts. We observe evidence for both direct and precursor-mediated chemisorption pathways. As expected, increasing En (or Ts) decreases S0 for the precursor-mediated reaction and increases S0 for the direct chemisorption. However, vibrational excitation of the incident SiH4 increases S0 for both the direct and the precursor-mediated pathway with a higher S0 for the |2000> state than for the |1100> state, indicating a nonstatistical reaction mechanism. [ABSTRACT FROM AUTHOR]

The reactivity of methane (CH(4)) on Pt(110)-(1 x 2) has been studied by quantum state-resolved surface reactivity measurements. Ground state reaction probabilities, S(0)(v=0) congruent with S(0)(laser-off), as well as state-resolved reaction probabilities S(0)(2nu(3)), for CH(4) excited to the first overtone of the antisymmetric C-H stretch (2nu(3)) have been measured at incident translational energies in the range of 4-64 kJ/mol. We observe S(0)(2nu(3)) to be up to three orders of magnitude higher than S(0)(v=0), demonstrating significant vibrational activation of CH(4) dissociation on Pt(110)-(1 x 2) by 2nu(3) excitation. Furthermore, we explored the azimuthal and polar incident angle dependence of S(0)(2nu(3)) and S(0)(v=0) for a fixed incident translational energy E(t)=32 kJ/mol. For incidence perpendicular to the missing row direction on Pt(110)-(1 x 2) and polar angles theta>40 degrees, shadowing effects prevent the incident CH(4) 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 x 2) reactivity that is dominated by top layer Pt atoms located at the ridge sites. A comparison of S(0)(v=0) measured on Pt(110)-(1 x 2) and Pt(111) yields a lower average barrier for Pt(110)-(1 x 2) by 13.7+/-2.0 kJ/mol.

The quantum state-resolved reactivity S(0) of SiH(4) on Si(100)-2x1 has been measured for the first time for two vibrationally excited Si-H stretch local mode states (mid R:2000 and mid R:1100) as well the ground state S(0) as a function of translational energy E(n) and surface temperature T(s). We observe evidence for both direct and precursor-mediated chemisorption pathways. As expected, increasing E(n) (or T(s)) decreases S(0) for the precursor-mediated reaction and increases S(0) for the direct chemisorption. However, vibrational excitation of the incident SiH(4) increases S(0) for both the direct and the precursor-mediated pathway with a higher S(0) for the mid R:2000 state than for the mid R:1100 state, indicating a nonstatistical reaction mechanism.