Symmetry-resolved CO desorption and oxidation dynamics on O/Ru(0001) probed at the C K-edge by ultrafast x-ray spectroscopy.
Symmetry-resolved CO desorption and oxidation dynamics on O/Ru(0001) probed at the C K-edge by ultrafast x-ray spectroscopy.
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通过超快 X 射线光谱在 C K 边缘探测 O/Ru(0001) 的对称解析 CO 解吸和氧化动力学。
DOI：
10.1063/5.0114399
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
A. Nilsson
中科院分区：
文献类型：
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作者：
J. LaRue;Boyang Liu;Gabriel L. S. Rodrigues;Changle Liu;Jose A. Garrido Torres;S. Schreck;Elias Diesen;M. Weston;H. Ogasawara;F. Perakis;M. Dell’Angela;F. Capotondi;Devon Ball;Conner Carnahan;Gary Zeri;L. Giannessi;E. Pedersoli;D. Naumenko;P. Amann;I. Nikolov;L. Raimondi;C. Spezzani;M. Beye;J. Voss;Hsin‐Yi Wang;F. Cavalca;J. Gladh;Sergey Koroidov;F. Abild;M. Kolb;P. Miedema;Roberto Costantini;T. Heinz;A. Luntz;L. Pettersson;A. Nilsson
我们报告的一氧化碳解吸和氧化诱导的400 nm飞秒激光激发的O/Ru（0001）表面探测的时间分辨X射线吸收光谱（TR-XAS）在碳K边。实验在CO（6 × 10-8 Torr）和O2（3 × 10-8 Torr）的恒定背景压力下进行。在这些条件下，我们检测到两个短暂的CO物种与窄的2π* 峰，表明很少与表面的2π* 相互作用。基于极化测量，我们发现这两种物质具有相反的取向：（1）CO有利于更垂直的取向和（2）CO有利于更平行于表面的取向。我们还使用质谱仪直接检测气相CO2，并在略高于2π* 区域的X射线能量下观察到弯曲吸附CO2的微弱特征。将这些结果与先前报道的在O K边缘的TR-XAS结果进行比较，其中CO背景压力低三倍（2 × 10-8 Torr），同时保持相同的O2压力。在较低的CO压力下，在CO2 π* 区域，我们观察到吸附的CO和接近CO氧化过渡态的OC-O键长分布，几乎没有气体状CO的迹象。向“气体状”CO物种的转变可以解释为较高的CO暴露，这阻止了O吸附，降低了O覆盖度，增加了CO覆盖度。这些效应通过偶极-偶极相互作用降低CO解吸势垒，同时增加CO氧化势垒。
We report on carbon monoxide desorption and oxidation induced by 400 nm femtosecond laser excitation on the O/Ru(0001) surface probed by time-resolved x-ray absorption spectroscopy (TR-XAS) at the carbon K-edge. The experiments were performed under constant background pressures of CO (6 × 10-8 Torr) and O2 (3 × 10-8 Torr). Under these conditions, we detect two transient CO species with narrow 2π* peaks, suggesting little 2π* interaction with the surface. Based on polarization measurements, we find that these two species have opposing orientations: (1) CO favoring a more perpendicular orientation and (2) CO favoring a more parallel orientation with respect to the surface. We also directly detect gas-phase CO2 using a mass spectrometer and observe weak signatures of bent adsorbed CO2 at slightly higher x-ray energies than the 2π* region. These results are compared to previously reported TR-XAS results at the O K-edge, where the CO background pressure was three times lower (2 × 10-8 Torr) while maintaining the same O2 pressure. At the lower CO pressure, in the CO 2π* region, we observed adsorbed CO and a distribution of OC-O bond lengths close to the CO oxidation transition state, with little indication of gas-like CO. The shift toward "gas-like" CO species may be explained by the higher CO exposure, which blocks O adsorption, decreasing O coverage and increasing CO coverage. These effects decrease the CO desorption barrier through dipole-dipole interaction while simultaneously increasing the CO oxidation barrier.