Probing the electronic structures of low oxidation-state uranium fluoride molecules UFx− (x = 2−4)

Abstract

We report the experimental observation of gaseous UF(x)(-) (x = 2-4) anions, which are investigated using photoelectron spectroscopy and relativistic quantum chemistry. Vibrationally resolved photoelectron spectra are obtained for all three species and the electron affinities of UF(x) (x = 2-4) are measured to be 1.16(3), 1.09(3), and 1.58(3) eV, respectively. Significant multi-electron transitions are observed in the photoelectron spectra of U(5f(3)7s(2))F2(-), as a result of strong electron correlation effects of the two 7s electrons. The U-F symmetric stretching vibrational modes are resolved for the ground states of all UF(x) (x = 2-4) neutrals. Theoretical calculations are performed to qualitatively understand the photoelectron spectra. The entire UF(x)(-) and UF(x) (x = 1-6) series are considered theoretically to examine the trends of U-F bonding and the electron affinities as a function of fluorine coordination. The increased U-F bond lengths and decreased bond orders from UF2(-) to UF4(-) indicate that the U-F bonding becomes weaker as the oxidation state of U increases from I to III.

Photoelectron spectroscopy and theoretical studies of gaseous uranium hexachlorides in different oxidation states: UCl6q− (q = 0–2)

“…24 Relevant to the current uranium halides, we have successfully applied ESI-PES to probe the electronic structures of a series of uranyl and uranium halide anions in conjunction with relativistic quantum chemical calculations. [25][26][27][28][29][30][31] In particular, we have produced [UF 5 ] − and [UF 6 ] − using ESI and obtained the PES spectra of [UF 5 ] − both at room temperature and low temperature, which yielded an accurate electron affinity (EA) for UF 5 as 3.885 ± 0.015 eV. 28,29 The [U(f 2 )F 5 ] − anion has a C 4v symmetry with two unpaired 5f electrons, occupying f z 3 and f xyz type orbitals, respectively.…”

A combined photoelectron spectroscopy and relativistic ab initio studies of the electronic structures of UFO and UFO−

“…Our previously observed U-O stretching frequency for UO 2 was 856 cm −1 , 24 whereas the U-F stretching frequency observed for UF 2 was about 580 cm −1 . 22 Thus, the observed vibrational spacing of 640 cm −1 in band A is likely due to the U-F stretching mode in UFO. The band B observed at 1.84 eV and band C at 2.04 eV are weak and broad, which may each contain many detachment transitions.…”

“…25 The UFO − anion was produced as a contaminant during experiments on UF x − anions. 22 In brief, a uranium disk target was ablated by a pulsed laser in the presence of a helium carrier gas containing a small amount of F 2 . Plasma reactions between the laser-vaporized uranium atoms and F 2 produced various UF x − species.…”

“…Plasma reactions between the laser-vaporized uranium atoms and F 2 produced various UF x − species. 22 However, because of oxide contamination on the target surface, strong UFO − anion signals were observed along with UF 2 − and UO 2…”

“…The UFO − and UFO systems are isoelectronic with U()F 2 and U()O 2 − , respectively, which have been studied extensively. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Therefore, the photoelectron spectra of UFO − should be very helpful to obtain information about the ground state as well as low-lying excited states of UFO neutral. Experimental vertical detachment energies (VDEs) are compared with the theoretical calculation of the ground and many low-lying excited electronic states of neutral UFO in order to interpret the experimental findings from the UFO − spectra.…”