The vibrational spectra of a molecule and related molecular crystal are systematically analyzed theoretically with the account of the influence of anharmonic interactions between the vibrations. The specific anharmonism‐induced features in the spectra of a molecule and crystal are revealed, and spectral lineshapes at varied strength of anharmonic interaction are simulated. The proposed general theoretical approach is used for fitting the experimental vibrational spectra of CO2 substance in gas and molecular crystal phases. Pretty good coincidence of experimental data with theoretical results is demonstrated, and the constants of anharmonic interaction are obtained. The proposed theoretical approach can be used to interpret the bands in the Raman and infrared absorption spectra of various complex molecules and crystals.

This work describes fabrication and characterization of two types of surfaceenhanced Raman scattering (SERS) substrates based on starlike gold nanoparticles (NPs). Type I SERS substrates are formed by adsorption of gold nanoparticles from chemically synthesized colloidal solution onto the modified glass substrates. Type II SERS substrates are fabricated by the direct nucleation and growth of Au NPs on the modified glass substrates immersed in the precursors solution. Morphology, optical, and SERS characteristics of both types of substrates are studied. Study shows that by varying the diameters of nanostars cores and the lengths of their spikes during the synthesis one can tune the plasmon absorption peak position from visible to near-infrared and achieve the resonance with most of common laser wavelengths. The measured SERS enhancement factors are equal to 10 5 and 10 6 for the substrates of type I and type II, respectively. The modeling of the electric field distribution in the vicinity of nanoparticles are done for exciting laser wavelengths varied in the range from 400 to 1000 nm. Calculated electric field distribution in the vicinity of Au NPs at different λ exc correlates with the SERS enhancement factors obtained experimentally.

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The affordable and scalable synthesis of noble metal nanoparticles that are biocompatible without additional functionalization steps has been a growing field of research, stimulated by numerous prospective applications of these NPs. In the case of phytosynthesized or biogenic noble metal NPs, the mechanism of NP stabilization by biomolecules contained in each particular plant extract or living organism determines the possible applications of these NPs. In this work, we investigated Ag NPs synthesized in water with plant extracts of common toothwort (Lathraea squamaria) and two species of pepper (Capsicum annuum and Capsicum chinense). From FTIR and XPS, we drew conclusions about the composition of the functional groups and molecules that stabilize NPs in each extract, such as polysaccharide compounds (pectins, cellulose, glycosides and phenolic acids). Distinct characteristic IR features of amide I and amide II proteins were observed, which are common in plant extracts, while features of amide III were not distinctly observed in our extracts. A Raman spectroscopy study revealed weak own-SERS activity of the biomolecules of the extract and high efficiency of the NPs in the enhancement of “external” analytes, such as dyes and antibodies. This is the first report of the efficient SERS application of phytosynthesized Ag NPs.