Abstract: Objective To investigate selectivity to excitation wavelength of Raman spectra for several compounds.Methods We obtained the different Raman spectra of some samples with different excitation,mainly including salicylic acid(SA),p-methoxybenzoic acid(p-MBA) and metronidazole.Results The Raman spectra of SA and p-MBA in aqueous solution were correspondent to their solid counterpart at ultraviolet excitation,which could not be observed with visible or near infrared excitation.The high-quality Raman spectra of metronidazole were obtained with visible and near infrared light while there was not any Raman band with ultraviolet.Conclusion The spectra of SA and p-MBA demonstrate the advantages of ultraviolet excitation,but on the other hand the spectra of metronidazole indicate the selectivity of excitation wavelength.

Key words: Raman, salicylic acid, p-methoxybenzoic acid, metronidazole