Jason T. Yustein

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

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/A and Frr=0.12 mdyn/A 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.

Pulsed laser evaporation of boron/carbon pellets: Infrared spectra and quantum chemical structures and frequencies for BC2

Pulsed laser evaporation of pellets pressed from boron and graphite powder gave a new 1:4 doublet at 1232.5 and 1194.6 cm−1 in addition to the carbon cluster absorptions reported previously. The 1232.5 cm−1 band dominated boron‐10 experiments. The new bands increased as carbon cluster bands decreased with increasing B/C ratio in the pellet and with increasing laser power. Augmented coupled cluster and full‐valence complete active space SCF (CASSCF) calculations predict the global minimum BC2 structure to be an asymmetric triangle: however, the vibrationally averaged structure will be an isosceles triangle with a strong symmetric B–C2 stretching frequency near 1200 cm−1. The calculated boron‐10/boron‐11 frequency ratio (1.0323) is in excellent agreement with the observed ratio (1.0317), and confirms assignment of the 1194.6 cm−1 band to the BC2 ring. Calculations predict linear BCC to be less stable by 6.2±2 kcal/mol and to absorb in the 2000–2050 cm−1 range: the barrier towards rearrangement to the cyclic...

Reactions of pulsed-laser evaporated lithium atoms with O2 and N2O

Abstract Pulsed laser evaporated Li atoms were codeposited with O2 in excess argon at 12 K. The same LiO2 and LiO2Li products were observed that were formed with thermal Li atoms. However, with N2O the LiO product was observed in contrast to thermal Li atom reactions. Excess kinetic energy in the laser evaporated Li atoms provided activation energy for the abstraction reaction. In addition the extremely large yield of O4− observed in O2 experiments provides evidence for photoelectron emission from the lithium metal surface.

Matrix isolation infrared spectra of O2 and N2 insertion reactions with atomic uranium

Laser ablation of refractory metals can be an effective source of vapor for matrix isolation IR studies. This combination of techniques was used for the first time to study the mechanisms of U vapor reactions with atmospheric components. U atoms and O2 were codeposited with excess Ar at 12 K. The dominant codeposition products were UO2 and UO3. In contrast, the UO yield was always small because UO2 is formed by an insertion mechanism. This mechanism was verified in the 16O2/18O2 experiments which failed to produce 16OU18O. The effects of UV photolysis and matrix annealings were also examined. The U atoms and O2 reaction requires little or no activation energy since UO2 was formed from cold reagents. New charge‐transfer species, (UO2+2)(O2−2) and (UO+2)(O−2), and a weak complex, UO3–O2, were primarily produced under conditions which favored further O2 reactions. Similar U atom and N2 experiments produced only linear NUN which is also produced by an insertion mechanism. This U reaction represents the first ...