Holman Jasper, Davies Paul B, Nishida Takuma, Ye Shen, Neivandt David J
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK.
J Phys Chem B. 2005 Oct 13;109(40):18723-32. doi: 10.1021/jp051564y.
Sum frequency generation (SFG) vibrational spectra of cadmium arachidate multilayer films adsorbed on a substrate with high nonresonant susceptibility, i.e., gold, and on a low nonresonant susceptibility substrate, i.e., fused quartz, have been investigated in the C-H stretching region in air. The films were formed by Langmuir-Blodgett (LB) deposition and their spectra recorded using SFG spectrometers employing both 532-nm nanosecond and 800-nm femtosecond lasers, with counter-propagating and co-propagating beam geometries, respectively. Both kinds of substrate were rendered hydrophobic by coating them with per-deuterated octadecanethiol (gold) or per-deuterated cadmium arachidate (fused quartz) monolayers. Single per-protonated arachidate layers in otherwise per-deuterated 10-layer films were used to show that the SFG resonances arise only from the topmost and lowermost layers in a LB film comprised of an even number of per-protonated layers, although the SFG spectra from the two hydrophobic substrates are different from each other. The differences in the spectra from the same ten-layer per-protonated films deposited on the two types of hydrophobic substrate have been explained in terms of a simple model that accounts for resonant and nonresonant contributions.
已在空气中的C-H伸缩振动区域研究了吸附在具有高非共振磁化率的基底（即金）和低非共振磁化率基底（即熔融石英）上的花生酸镉多层膜的和频振动光谱。这些膜通过朗缪尔-布洛杰特（LB）沉积法形成，其光谱使用分别采用532 nm纳秒激光和800 nm飞秒激光的和频光谱仪记录，光束几何结构分别为反向传播和同向传播。通过用全氘代十八烷硫醇（金）或全氘代花生酸镉（熔融石英）单层涂覆两种基底，使其具有疏水性。在其他方面为全氘代的10层膜中使用单质子化花生酸层来表明，和频共振仅来自由偶数个单质子化层组成的LB膜的最顶层和最底层，尽管来自两种疏水基底的和频光谱彼此不同。已根据一个考虑共振和非共振贡献的简单模型解释了沉积在两种疏水基底上的相同十层单质子化膜的光谱差异。
