The results of investigation of the absorption spectra of ascorbic acid solutions with varying pH value are presented. The acidity of the solutions changed with increasing concentration, with the addition of hydrogen peroxide and sodium hydroxide. It was found that the position of the maximum absorption of ascorbic acid solutions depends on the pH value. The position of the absorption maxima shifts from 243 nm to 268 nm if the pH increases from 2 to 9. The change in the spectra is due to the stronger oxidation of ascorbic acid in alkaline solutions, which is accompanied by the removal of protons.
The paper presents the results of a study of photoinduced disturbances in the operation of polarizing optical devices based on a lithium niobate crystal.. Significant changes were found in the modulation dependences of the electro-optical modulator with increasing intensity and time of irradiation. The intensities of photoinduced electric fields and changes in the electro-optical coefficients of the crystal are determined.
The results of the experimental research of the change in the absorption spectra of ascorbic acid solutions with the addition of stabilizer NaHCO3 have been presented. It was shown that L-ascorbic acid is degraded in an aqueous solution, which causes a change in its absorption spectrum. The use of sodium bicarbonate as a stabilizer did not significantly change the absorption spectrum of chemically pure ascorbic acid in the range of 200-300 nm. The obtained results allow to control the concentration and conditions of application of these stabilizers.
The results of molecular modeling of ascorbic acid electronic spectra in different solutions are represented. Geometric parameters and characteristics of electronic spectra of an isolated molecule and a molecule in solutions are determined within the framework of two models of solvation. It was shown that the increase of the dipole moment and the dielectric constant of the solvent leads to shift in the spectral bands and a change of the oscillators strength of the electronic transitions.
The results of numerical calculations of IR absorption and Raman spectra of ascorbic acid in polar and nonpolar solutions are presented. The dependence of the change in the total energy and the dipole moment of the molecule on the characteristics of the solvents was investigated using the two solvation models. Spectral bands and the corresponding structural groups of the molecule are found, the characteristics of which are most vulnerable to solvents.
The results of research the changes in the absorption spectra of aqueous solutions of ascorbic acid under the influence of laser radiation are presented. The solutions were irradiated with the radiation of semiconductor lasers with wavelengths of 408 and 532 nm, YAG: Nd3+ laser with a wavelength of 1064 nm and a nitrogen laser with a wavelength of 337.1 nm. The photoinduced changes in the spectrum are revealed, which indicate the breakage of π → π bonds in the molecule of ascorbic acid during its destruction.
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