MATRIX INFRARED-SPECTRA OF NUN FORMED BY THE INSERTION OF URANIUM ATOMS INTO MOLECULAR NITROGEN

Pulsed-laser ablated uranium atoms were codeposited with N-14(2)(N-15(2)) and excess Ar at 12 K. The Fourier transform infrared (FTIR) spectrum revealed a single product, UN2, which exhibited a v3 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 (NN)-N-14-N-15 experiments the v1 and v3 modes of (NUN)-N-14-N-15 were observed at 987.2 and 1040.7 cm-1, respectively; FG matrix calculations were performed to determine F(r) = 8.27 mdyn/angstrom and F(rr) = 0.12 mdyn/angstrom and to estimate the IR-inactive v1 modes of (UN2)-N-14 and (UN2)-N-15 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.