Raman and surface Raman spectroscopy with ultraviolet excitation

We record the accurate and reliable Raman spectra of benzoic acid (BA), p-nitrobenzoic acid (PNBA) and o-nitrobenzoic (ONBA) in aqueous solution with ultraviolet excitation. And we find that the ultraviolet (UV) Raman spectrum of aqueous BA solution has one-to-one correspondence to that of BA solid whereas the others are less resemble to the solid counterparts. We also report surface Raman spectroscopy of them in silver colloid without any enhancement in UV region and call it surface-unenhanced Raman spectroscopy (SUERS) while the surface-enhanced Raman scattering (SERS) effects are perfect in near infrared or visible regions. It demonstrates the SERS effects are strongly dependent on the excitation wavelength. On the basis of the experiments, we discuss the mechanism of SERS excited in different regions.