Measurements of the isotopic composition of UF6 according to the fine structure of the IR absorption spectrum in the ν1 + ν3 band

Absorption spectra of the Q -branch of the ν 1 + ν 3 vibrational–rotational band of uranium hexafluoride (UF 6 ) recorded in a range of 1290.0–1292.5 cm –1 using a laser spectrometer based on a quantum cascade laser have been studied. The spectra of samples with a natural isotopic composition (0.7% U 235 ), an enriched sample (90% U 235 ), and their gas mixtures (2, 5, and 20% U 235 ) in a pressure range of 10–70 Torr at a temperature of T = 296 K have been analyzed. The experiments have revealed a highly reproducible fine structure of the recorded spectra. Periodic singularities in the fine-structure spectra have been interpreted as a manifestation of hot band transitions near the Q -branch. Anharmonicity constants X 21 , X 31 , and X 32 and their combinations X i1 + X i3 ( i = 4, 5, 6) have been determined. The characteristic features in the fine-structure spectra and the initial spectrum have been used to determine the isotopic composition of enriched UF 6 samples.