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 nu(1) + nu(3) vibrational-rotational band of uranium hexafluoride (UF6) 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 UF6 samples.