Real Time Observation of Surface Chemical Reaction by Nonlinear Spectroscopy

结合强近红外（NIR）脉冲辐照引起的快速温升和振动和频产生（SFG）光谱技术（一种表面敏感的超快光谱技术），可以观察与热激发有关的表面动力学。本研究将这种时间分辨方法应用于甲氧基(CH_3O-)/Ni（111）和C_6H_<12>（环己烷）/Ni（111）表面体系。在C_6H_<12>/Ni（111）体系中，近红外脉冲辐照引起Ni（111）表面温度的短暂跃变，高覆盖态峰强度增强，低覆盖态峰强度减弱。结果表明，温度跃迁使环己烷分子从低覆盖态跃迁到高覆盖态。在(ch3o -)/Ni（111）体系中，假设基态的甲氧基处于化学平衡状态，而非瞬时加热产生的新状态，模拟再现了所观察到的时间分布。结果表明，250 K的温度变化会引起甲氧基在Ni（111）表面的分子取向或吸附位置的变化，而不会使甲氧基分解为吸附的CO和氢。在分子激发过程的控制上，采用优化的脉冲整形技术，提高了近红外（波长为800 nm）飞秒脉冲双光子激发苝分子的发射强度。结果表明，脉冲间隔约为100 fs的脉冲列形状比单飞秒脉冲的发射强度强。晶体样品和溶液样品优化后的脉冲形状非常相似，对晶体样品有效的脉冲形状对溶液样品也有效，反之亦然。结果表明，晶体样品和溶液样品的效率提高机制基本相同，在330 cm^<-1>附近的分子内振动模式（振荡周期约为100 fs）深入参与了激发过程。少

The surface dynamics concerned with thermal excitation can be observed by combining rapid temperature rise induced by irradiation of intense near-infrared (NIR) pulse and vibrational sum-frequency generation (SFG) spectroscopy which is surface sensitive and ultrafast spectroscopic technique. In this study, such time-resolved method was applied to methoxy (CH_3O-)/Ni(111) and C_6H_<12>(cyclohexane)/Ni(111) surface systems. On the C_6H_<12>/Ni(111) system, the irradiation with NIR pulses caused a temporary jump in temperature at the Ni(111) surface and enhanced the intensity of the peak from the high-coverage state, but weakened the peaks from the low-coverage state. It was concluded from the results that the temperature jump excites the cyclohexane molecules from the low-coverage state to the high-coverage state. On the (CH_3O-)/Ni(111) system, the observed temporal profile was reproduced by simulation assuming that the original methoxy in the ground state was in chemical equilibrium wi … More th a new state produced by instantaneous heating. It was concluded from the results that a temperature jump of 250 K induced a change in the molecular orientation or adsorption site of methoxy on the Ni(111) surface without decomposition of methoxy to adsorbed CO and hydrogen. On the control of excitation process of molecules, the optimized pulse shaping technique was applied to increase the emission intensity from perylene molecule induced by two-photon excitation using NIR (wavelength of 800 nm) femtosecond pulse. It was found that the pulse-train-like pulse shape with the pulse interval of about 100 fs showed the emission intensity stronger than that by a single femtosecond pulse. The pulse shapes optimized for crystalline and solution samples were very similar to each other, and the pulse shape effective for the crystalline sample was also effective for the solution sample and vice versa. It was concluded that the mechanism for the efficiency increase was essentially the same for the crystalline and solution samples, and that the intramolecular vibrational modes at around 330 cm^<-1> (oscillation period of about 100 fs) were deeply involved in the excitation process. Less