[en] Natural and synthetic diamonds of various types were studied. After irradiation of 10¹⁸ neutr./cm² of the 1b-type crystals the intensity of absorption band at 1200 cm^-1 increases, and new bands appear at 950, 1060 and 1332 cm^-1. After irradiation of 10¹⁹ neutr./cm^-2 the absorption in the one-phonon region (less than 1332 cm^-1) of diamond crystals of all types is the same. In the region of local oscillations bands are detected at 1420, 1535, 1570 cm^-1. In spectra of the 2b-type diamonds bands disappear at 2460 and 2810 cm^-1, and electric resistance grows for 3-6 orders of magnitude. At 1535 and 1570 cm^-1 bands disappear as a result of isochronous annealing up to 800 deg C, and at 1450 and 1510 cm^-1 absorption bands appear. In the temperature range of 300-60O deg C further increase of electric resistance of the 2b-type crystals is observed. The presence of negative annealing and new absorption bands at annealing gives evidence about partial annealing reconstruction of complicated defects of the type of disordering regions and reformation of simpler defects