Computational study of SERS effects in some aliphatic and cyclic carboxylic acids with silver nanomaterials

Quantum chemical calculations have been shown to provide convenient means in estimating surface-enhanced Raman scattering (SERS) spectral shifts and the adsorption possibilities associated with such shifts. In a recent work, the computed Raman spectra provided very good agreement with the experimental results for valeric acid. To attain a conclusive picture of the Raman shifts in related molecules, namely, butyric acid, caproic acid, γ-butyrolactone, γ-valerolactone and γ-caprolactone, full optimizations and frequency calculations have been carried out. The vibrational frequency shifts caused by the interaction of these molecules with the Ag₄ cluster simulate the experimental shifts with silver nanoparticles (AgNPs). The most prominent shift noticed is in the case of γ-caprolactone through its ether C-O-C group interacting with the silver cluster. Such a shift may be due to the +I effect of the alkyl side chains and corresponds to a theoretical interaction energy and distance of -12.92 kcal/mol and 2.45Å, respectively.