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Using the density functional theory (DFT), we calculated the structures and Raman spectra of trans-isomers of α-carotene, β-carotene, γ-carotene and lycopene as well as trans-isomers of modified β-carotene and lycopene molecules with substituted end or/and side groups. The DFT calculations showed that the position of the CC stretching band depends mainly on the number of conjugated CC bonds and decreases with an increase in the conjugation length. The weak dependence of the position of the CC stretching band on the structure of the carotenoid side and end groups suggests that this band can be used to evaluate the conjugation length for trans-isomers of various molecules containing polyene chains. The CC stretching band shifts towards lower wavenumbers with growth of the conjugation length or masses of the end groups and to higher wavenumbers in the presence of the side CH

Raman spectra of liquid ethylene glycol (EG), 1,2-propylene glycol (1,2-PG) and 1,3-propylene glycol (1,3-PG) were analyzed in terms of the conformational composition of the molecules. The analysis was based on comparison of the experimental spectra with the results of the density functional theory (DFT) calculations of the structure, energy and Raman spectra for 10 conformations of EG molecule, 27 conformations of 1,2-PG molecule and 25 conformations of 1,3-PG molecule. The gas-phase approximation calculations well describe the main features of the experimental spectra of the liquid substances in the region 600 – 1600 cm−1. Calculations for clusters of EG molecules showed that an increase in the number of molecules in a cluster leads to significant improvement of the agreement between the calculated and experimental spectra. The conformations of molecules in the clusters are strongly distorted in comparison with the results of the gas-phase approximation. Thus, the intermolecular interactions influence significantly the conformational order and the Raman spectra of the diols.

We carried out calculations of non-resonance Raman spectra of s-carotene and polyenes CH2 (CH CH )n-2CH CH2 using the density functional theory (DFT). We revealed that the peak positions and intensities of the C C and C C stretching bands depend on length of the polyene chain and type of the isomer. Our experimental non-resonance Raman spectra of s-carotene powder match well the DFT-simulated Raman spectrum of s-carotene in the all-trans form. The peak positions and relative intensities of the C C and C C stretching bands of s-carotene turned out to be similar in the resonance and non-resonance Raman spectra. An increase in the number of conjugated double bonds (n = 3–30) in a polyene structure results in a monotonous shift of the positions of the most intense C C and C C bands towards lower wavenumbers with an increase in the band intensities. An increase in the isomer number results in the monotonous decrease of the C C stretching band intensity for polyenes with 9, 10, 11, 15 and 24 double bonds. An increase in the isomer number inhomogeneously influences the form, position and intensity of the C C stretching band.

Experimental Raman spectra of liquid and solid polyethylene glycols (PEGs) with various molecular weights were compared with the results of the density functional theory (DFT) calculations. The structure, energies and Raman spectra of molecules in the trans and 72 helical conformations with various orientations of the terminal groups were calculated for PEG molecule with 9 monomer units. Recorded spectrum of PEG with the average molecular weight of 400 Da (8–9 monomer units) matches very well the calculated spectrum of the most thermodynamically stable g’G(TTG)8g’ conformation. DFT-calculated Raman spectra for the g’G(TTG)ng’ conformation depend on the amount of the monomer units in PEG molecule. The peak position of the PEG Raman line at about 1100 cm−1 can be used to estimate the molecular weight distribution of short molecules.

Monitoring the transient buildup of laser emission is proposed as a simple method for spectro-temporal intracavity diagnostics of laser transitions and materials. Using this method, we determined the absolute magnitude of both laser emission and absorption cross sections for a line-narrowed tunable Er/sup 3+/-fiber laser. >