腺嘌呤、嘌呤和四并苯的表面增强拉曼光谱随温度的可逆变化

用硝酸腐蚀法处理得到了具有表面增强拉曼光谱 (SERS)活性的银表面。在表面温度于 - 1 90℃～30℃变化时 (上升和下降 ) ,分别测定了吸附在银表面上的腺嘌呤、嘌呤和四并苯的表面增强拉曼光谱 ,观察到一系列有关拉曼峰频率和强度的可逆变化。结果表明 ,温度降低 ,吸附分子SERS中受电磁增强机制作用的振动的拉曼位移发生蓝移 ,同时峰强度也有变化 ;而受化学增强机制作用的振动的拉曼位移则不受温度的影响。温度的变化导致分子平面可弯曲分子在金属表面的取向发生变化 ,如腺嘌呤和嘌呤在高温下取直立态 ,而平面的对称分子 (如四并苯 )在表面上的取向则不受温度的影响。

Reversible Temperature Dependence of Surface-Enhanced Raman Scattering of Adenine, Purine and Pyrene

The surface-enhanced Raman scattering (SERS) spectra of adenine, purine and pyrene adsorbed on a SERS-active silver surface roughened by nitric acid have been measured over the -190 degrees C-30 degrees C surface temperature range. The results show that the Raman shifts and SERS intensity of the vibrations, which are enhanced by electromagnetic mechanism, are affected by temperature, those by chemical mechanism are not. However, it has been found that the observed temperature dependence can be explained by postulating the reorientation of the absorbates. Adenine molecules and purine molecules prefer to adopt a more perpendicular stance on the surface at high temperature, but for a planar symmetric molecule, such as pyrene, the preferred orientation is parallel and temperature has no effect on its orientation.