Purpose. In our experiments, the luminescence spectra of different pH value guanine solutions and isolated molecules were obtained in the range of 200-500 nm under the action of slow electrons. The luminescence maximum is at 360 nm. For a weakly acidic solution, the luminescence maximum is observed in the range of 380 nm. For a slightly alkaline solution, the opposite is true. Here, the luminescence maximum shifts toward smaller wavelengths and is about 340 nm. It is clearly shown, that the luminescence maximum vastly depends from the pH value of the solution. The spectra in the article shows clear fluorescence, while phosphorescence is almost absent. The neutral environment changes the spectra only slightly. The spectrum has more than 20 spectral lines and zones, that were identified based on available literature. Methods. The photoluminescence of guanine solutions was studied optically using the high-sensitivity RF-6000 spectrofluorimeter from Shimadzu. Results. Photoluminescence spectra of guanine solutions with different pH values and luminescence spectra of isolated molecules after slow electron impact excitation in the wavelength range from 200 to 500 nm were obtained. Conclusions. It is shown that the given spectra of different solutions reflect only the fluorescence of guanine molecules, and phosphorescence is practically absent. Minimal effects on the luminescence spectra of guanine occur from a neutral medium. The interaction of slow electrons with guanine molecules in the gas phase is accompanied by the appearance of an emission spectra of complex shape in the range of 200-500 nm, which indicates intense fragmentation of guanine molecules

Keywords: luminescence, excitation, guanine, slow electrons, molecular zone