Study of electronic excited states of molecule absorbed surface by nonlinear spectroscopy

本研究采用非线性谱技术，如二次谐波产生谱（SHG）和和频产生谱（SFG），研究了分子吸附表面的电子激发态。利用基于Ti：蓝宝石再生放大系统的飞秒可调谐激光系统，在苯和CO吸附的Cu（111）表面，测量了250 ~ 700 nm SH波长区域的SHG光谱。在干净的Cu（111）表面发现了新的电子共振峰。其中一个峰是缺陷部位的电子态共振峰，另一个峰是亚单层苯吸附表面特有的电子态共振峰。采用和频产生法（SFG）和皮秒激光系统（时间分辨率为6 ps）对Ni（111）表面吸附的甲酸酯（HCOO）进行了时间分辨振动测量。当皮秒800 nm脉冲照射在样品表面时，观察到CH拉伸信号的强度在时间分辨率范围内快速下降，然后强度恢复（时间常数为几个10s ps）。从温度和泵浦流量对信号强度时间行为的依赖结果来看，我们认为所观察到的强度变化是由非热过程引起的。

In this research, electronic excited states of molecule adsorbed surfaces were studied by nonlinear spectroscopy, such as second harmonic generation (SHG) spectroscopy and sum frequency generation (SFG) spectroscopy. On benzene or CO adsorbed Cu(111) surfaces, SHG spectra of SH wavelength region from 250 nm to 700 nm were measured using femtosecond tunable laser system based on a Ti:sapphire regenerative amplifier system. The new electronic resonance peaks on the clean Cu(111) surface were found on the spectra. One of the peaks was assigned to the resonances between the electronic state on the defect sites and the other peak was assigned to the electronic state which is peculiar to the surface with sub-monolayer benzene adsorption. Time-resolved vibrational measurements were carried out on formate (HCOO) adsorbed on Ni(111) surface by combining the sum-frequency generation (SFG) method and picosecond laser system (time-resolution of 6 ps). Rapid intensity decreas (within the time-resolution) followed by intensity recovery (time-constant of several 10s ps) of CH stretching signal was observed when picosecond 800 nm pulse was irradiated on the sample surface. From the results of temperature and pump fluence dependences of temporal behavior of signal intensity, we concluded that the observed intensity change was induced by non-thermal process.