Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen

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Abstract
Pulsed‐laser ablated uranium atoms were codeposited with 14N2(15N2) and excess Ar at 12 K. The Fourier transform infrared (FTIR) spectrum revealed a single product, UN2, which exhibited a ν3 absorption at 1051.0 cm−1. Ultraviolet (UV) photolysis increased the yield of UN2 by threefold and showed that electronic excitation facilitated the insertion reaction. N2 perturbed UN2 bands at 1041.3 and 1031.5 cm−1 grew sharply during matrix annealings. In 14N15N experiments the ν1 and ν3 modes of 14NU15N were observed at 987.2 and 1040.7 cm−1, respectively; FG matrix calculations were performed to determine Fr=8.27 mdyn/Å and Frr=0.12 mdyn/Å and to estimate the IR‐inactive ν1 modes of U14N2 and U15N2 at 1008.3 and 985.7 cm−1, respectively. Energetic considerations suggest that the U+N2 insertion reaction has little exothermicity and that the activation energy for this reaction may be provided by hypothermal uranium atoms.