1. School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou 434023, China
2. College of Physical Science and Electronics, Central South University, Changsha 410012, China
3. Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China
Abstract：In this paper, Normal Raman Scattering (NRS) spectroscopy of o-hydroxybenzoic acid (OHBA) and Surface-enhanced Raman Scattering (SERS) spectroscopy of OHBA adsorbed on gold nanoparticles were studied. The spherical gold nanoparticles were prepared by chemical reduction method with gold chloride acid as precursor and trisodium citrate as reductant. The NRS spectroscopy of OHBA and the SERS spectroscopy of OHBA adsorbed on gold nanoparticles were collected by laser Raman spectrometer, and the laser beam (785nm) was used as the excitation light source. Meanwhile, density functional theory (DFT) method at the B3LYP/6-31+G**(C, H, O)/LANL2DZ(Au) level was used to optimize molecular configurations of o-hydroxybenzoic acid. Base on the optimized structure, the NRS spectroscopy of OHBA and the SERS spectroscopy by different adsorption configurations of OHBA adsorbed on gold nanoparticles were all calculated. Compared with the experimental data, the results showed that the calculation results using OHBA molecular adsorption configuration through carboxyl were much more matched with the experimental values than those of using OHBA molecules adsorption configurations through hydroxyl. At the end, comprehensive assignments of the vibration mode for OHBA were studied by GaussView. According to the identification analysis of OHBA molecular Raman peaks, it could be drawn that, in gold colloids, the OHBA molecule would be tipsily adsorbed on the surface of gold nanoparticles through the carboxyl. The visualization software displayed the structure characteristics and molecular group vibration of this molecular and provided important basis for assigning the vibrational peaks. This work has important effect on the further applications of o-hydroxybenzoic acid in biomedicine and other fields.
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