Surface Enhanced Hyper-Raman Spectroscopy SEHRS

13 Surface Enhanced Hyper-Raman Spectroscopy (SEHRS) 

Instrumentation. Instmmentation in the reported investigations is similar to that employed in SERS [497]. A powerful laser system is employed. In a study of pyrazine and pyridine adsorbed on a roughened silver electrode, it was observed, that spectra measured with adsorbed centrosymmetric pyrazine showed additional bands that were not observed with SERS [497]. With the non-centrosymmetric pyridine, the SEHR spectra were very similar to the respective SER spectra no new bands were found. Surface enhanced hyper-Raman spectra were found to be more sensitive (than SERS) towards interaction between the adsorbate and the surface. This is illustrated in vibrational spectra of bis(4-pyridine)acetylene (BPA) adsorbed on a silver electrode [497]. 

Because of the floating boundaries between SRS and SERS (e.g. simply roughening an electrode may already yield the shift from the former to the latter), numerous authors simply claim to have performed SERS without providing any supporting arguments. In the present case, the nanostructuring most likely provided EM enhancement. 

In a study of phenazine adsorbed on a silver electrode that employed both SERS and SEHRS, the electroreduction product of phenazine and the reduction intermediates could be identified [499]. In a comparative study with SERRS and resonantly enhanced hyper-Raman spectroscopy SERHRS, several dyes adsorbed on a roughened silver electrode were investigated [500]. According to the results, the efficiency 

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Surface Enhanced Hyper-Raman Spectroscopy (SEHRS) Hyper-Raman scattering is a nonlinear three-photon energy conversion process, that offers complementary informahon to Raman spectroscopy and has some advantages... 

The discovery and understanding of SERS was important not only because it made Raman a more viable analytical method but also because it introduced the concept of surface-enhanced spectroscopies in general. With the SERS precedent, surface-enhanced resonance Raman spectroscopy (SERRS) and surface-enhanced hyper-Raman spectroscopy (SEHRS) have both been discovered and put to use as analytical tools. In fact, enhancement factors as large as 10 have been measured in SEHRS experiments (see Section VII.B). This immense enhancement was only recently surpassed by the 10 " enhancement measured in single molecule SERS (see Section X). 

SEHRS Surface enhanced hyper-Raman spectroscopy scattering... 

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