Electronic Spectroscopy of UO₂Cl₂ Isolated in Solid Ar

Abstract

Laser-induced fluorescence spectra have been recorded for uranyl chloride isolated in a solid Ar matrix. Pulsed excitation was examined using a XeCl excimer laser (308 nm) and a dye laser operating in the 19500-27500 cm-1 range. Several absorption and emission band systems were observed. The emission spectra were characterized by a nearly harmonic vibrational progression with a frequency of 840 cm-1 starting at 20323 cm-1. The electronic absorption spectra were dominated by five harmonic vibrational progressions with frequencies of approximately 710 cm-1. Comparisons with theoretical calculations indicate that all of the transitions observed were associated with the UO2+2 subunit. They involved the promotion of an electron from a bonding orbital to the metal-centered 5f(delta) and 5f(phi) orbitals. Band origins and vibrational constants for five excited states were obtained. Fluorescence was observed from the lowest-energy excited state alone, regardless of the excitation wavelength. The decay curve was found to be biexponential, with characteristic decay lifetimes of 50 and 260 micros.

Speciation Studies of Metals in Trace Concentrations: The Mononuclear Uranyl(VI) Hydroxo Complexes

“…With their sensitivity toward complexation, it is clear that emission spectra should reflect structural information. For spectra recorded at low temperature (<20 K) a correlation of luminescence spectra and symmetrical stretching frequencies (Raman spectroscopy) was successfully demonstrated for aqueous as well as solid samples. − A transfer of this knowledge to systems at moderate temperatures is challenging and is therefore still missing. The approach proposed here attempts to improve this situation.…”

Probing the Electronic Structure and Chemical Bonding in Tricoordinate Uranyl Complexes UO2X3– (X = F, Cl, Br, I): Competition between Coulomb Repulsion and U–X Bonding

“…Uranyl species tend to retain low CN eq in the gas phase due to increased Coulomb repulsion between the ligands. Indeed, uranyl complexes exist in low-temperature noble-gas matrices in the form of neutral UO 2 X 2 (X = F, Cl, Br) species. − Recently, Groenewold et al measured the infrared multiphoton dissociation spectroscopy (IRMPD) of UO 2 X 3 – (X = F, Cl, Br, I) in the gas phase . We observed stable UO 2 F 4 2– and UO 2 Cl 4 2– dianions and their solvation complexes with water and acetonitrile molecules in the gas phase using electrospray ionization (ESI), , but UO 2 Br 4 2– and UO 2 I 4 2– were not observed in these experiments.…”

Excitation Energies of UO22+, NUO+, and NUN Based on Equation-of-Motion Coupled-Cluster Theory with Spin–Orbit Coupling

“…UO 2 2+ is the most common building block of larger uranium complexes, but it is difficult to be formed in gas phase and experimental spectroscopic measurements are carried out in aqueous solution and in crystals. Its environment will inevitably affect its excitation energies and theoretical investigation on related molecules such as [UO 2 Cl 2 ] , and [UO 2 Cl 4 2– ] − have been reported. On the other hand, calculating excitation energies of the bare UO 2 2+ can still provide useful information.…”