Spectroscopic and theoretical studies of UN and UN+

Abstract

The low-energy electronic states of UN and UN+ have been examined using high-level electronic structure calculations and two-color photoionization techniques. The experimental measurements provided an accurate ionization energy for UN (IE = 50 802 ± 5 cm−1). Spectra for UN+ yielded ro-vibrational constants and established that the ground state has the electronic angular momentum projection Ω = 4. Ab initio calculations were carried out using the spin–orbit state interacting approach with the complete active space second-order perturbation theory method. A series of correlation consistent basis sets were used in conjunction with small-core relativistic pseudopotentials on U to extrapolate to the complete basis set limits. The results for UN correctly obtained an Ω = 3.5 ground state and demonstrated a high density of configurationally related excited states with closely similar ro-vibrational constants. Similar results were obtained for UN+, with reduced complexity owing to the smaller number of outer-shell electrons. The calculated IE for UN was in excellent agreement with the measured value. Improved values for the dissociation energies of UN and UN+, as well as their heats of formation, were obtained using the Feller–Peterson–Dixon composite thermochemistry method, including corrections up through coupled cluster singles, doubles, triples and quadruples. An analysis of the ab initio results from the perspective of the ligand field theory shows that the patterns of electronic states for both UN and UN+ can be understood in terms of the underlying energy level structure of the atomic metal ion.

Experimental and Computational Description of the Interaction of H and H– with U

“…Several computational studies have been reported for uranium-containing diatomic molecules. − The electronic structure of uranium monohydride (UH) resembles those of UF and UCl, which can be considered ionic U + X – ; the uranium cation is perturbed by a closed-shell anion ligand. Bross and Peterson obtained a 4 I 9/2 (U + (5f 3 7s 2 ) ground state for UF and UCl from high-level correlated molecular orbital theory calculations, in agreement with previous calculations on UF by Antonov and Heaven using the CASPT2-SO approach.…”

Physics-Guided Curve Fitting for ab Initio Diatomic Spectroscopy

“…Polynomials remain a popular choice of model function. [13] In the present strategy, we include a high-resolution potential energy function computed using a less expensive, presumably lower-level theoretical method. This provides the physics used to guide the interpolation of the high-level data.…”

Photodissociation and Infrared Spectroscopy of Uranium–Nitrogen Cation Complexes

“…New approaches in synthetic chemistry have produced a variety of ligated uranium–nitrogen complexes. − Isolated uranium nitrides and uranium–nitrogen complexes have been studied with infrared spectroscopy of species produced in rare gas and nitrogen matrixes. − Unfortunately, gas phase spectroscopy on uranium–nitrogen compounds is quite limited. The UN diatomic has been studied by using resonant photoionization spectroscopy. , Bowen and co-workers recently reported the photoelectron spectrum of the uranium dinitride anion . This study revealed a closed-shell electronic structure for the corresponding neutral with uranium in the +6 oxidation state, isoelectronic with the uranyl cation.…”

“…The UN diatomic has been studied by using resonant photoionization spectroscopy. 46,47 Bowen and co-workers recently reported the photoelectron spectrum of the uranium dinitride anion. 48 This study revealed a closed-shell electronic structure for the corresponding neutral with uranium in the +6 oxidation state, isoelectronic with the uranyl cation.…”