Two dimethoate analogues-dimethoate and omethoate, are characterized by vibrational spectroscopy-FT-Raman and FTIR, and surface enhanced Raman scattering (SERS) on the substrate of Au/Ag core-shell nanoparticle. The vibrational peaks are assigned, and the vibrational mode and peaks’ shift resulting from different inner structures P＝S and P＝O in molecules of two dimethoate analogues are also analyzed at acidic and basic conditions. From the vibrational spectra, these groups ν(NH), ν_s(CH₂), ν(C—O), ν(O＝C—N) II, ν(S—CH₂), ν(P＝O) and ν(P＝S) in the analogues present notable different vibrational peaks, except for 690 cm^－1 ν(P＝O) and 650 cm^－1 ν(P＝S), while the peaks of ν_as(CH₃), ν(P—O—C), ν(O＝C—N) I, δ(CH₃), ν(C—C), ν(C—C＝O) are almost corresponding. The relationships of concentrations, pH values and hydrolysis processes in acidic and basic condition, to dimethoate analogues’ SERS are further discussed, and the analogues’ adsorption status on the Au/Ag core-shell nanoparticle surface are also speculated with SERS mechanisms and TEM.

Key words: dimethoate, omethoate, surface enhanced Raman scattering (SERS), adsorption