Photoelectron spectroscopy and theoretical studies of UF5− and UF6−

Abstract

The UF(5)(-) and UF(6)(-) anions are produced using electrospray ionization and investigated by photoelectron spectroscopy and relativistic quantum chemistry. An extensive vibrational progression is observed in the spectra of UF(5)(-), indicating significant geometry changes between the anion and neutral ground state. Franck-Condon factor simulations of the observed vibrational progression yield an adiabatic electron detachment energy of 3.82 ± 0.05 eV for UF(5)(-). Relativistic quantum calculations using density functional and ab initio theories are performed on UF(5)(-) and UF(6)(-) and their neutrals. The ground states of UF(5)(-) and UF(5) are found to have C(4v) symmetry, but with a large U-F bond length change. The ground state of UF(5)(-) is a triplet state ((3)B(2)) with the two 5f electrons occupying a 5f(z3)-based 8a(1) highest occupied molecular orbital (HOMO) and the 5f(xyz)-based 2b(2) HOMO-1 orbital. The detachment cross section from the 5f(xyz) orbital is observed to be extremely small and the detachment transition from the 2b(2) orbital is more than ten times weaker than that from the 8a(1) orbital at the photon energies available. The UF(6)(-) anion is found to be octahedral, similar to neutral UF(6) with the extra electron occupying the 5f(xyz)-based a(2u) orbital. Surprisingly, no photoelectron spectrum could be observed for UF(6)(-) due to the extremely low detachment cross section from the 5f(xyz)-based HOMO of UF(6)(-).

Note: Photoelectron spectroscopy of cold UF5−

“…However, we are confident about this assignment on the basis of the Franck-Condon simulations and theoretical calculations reported in our recent RT study. 1 Taking into account of the accuracy of the calibration, we report the EA of UF 5 as 3.885 ± 0.015 eV, which is significantly improved relative to the value obtained in our recent RT study or the estimate of 4 ± 0.4 eV using charge transfer. 9 The U-F vibrational frequency obtained from the low temperature data is the same as before.…”

“…9 The U-F vibrational frequency obtained from the low temperature data is the same as before. 1 In conclusion, we have measured photoelectron spectra of vibrationally cold UF 5 − and obtained a more accurate EA for UF 5 as 3.885 ± 0.015 eV.…”

“…1 Both UF 5 − and UF 5 were known to have C 4v symmetry, derived from the removal of one F atom from the octahedral UF 6 . But there is a large U-F bond length change between the ground states of the anion and neutral UF 5 , resulting in a long vibrational progression in the photoelectron spectra.…”

“…The electrospray conditions to produce the UF 5 − anions were identical to the previous room temperature study. 1 Figures 1(a)-1(c) display the photoelectron spectra of UF 5 − at three different detachment photon energies with the ion trap operated at 4.4 K, compared to the corresponding RT spectra (Figs. 1(d)-1(f)).…”

A computational study of adsorption and vibrations of UF6 on graphene derivatives: Conditions for 2D enrichment

“…Simultaneously, the U-F bonds interacting with graphene lengthen from 2.05 to 2.11 Å (the difference in U-F bond length between DFT and DFT-D are below 0.01 Å , and therefore only DFT values are reported). The bond lengthening is due to an increase in the occupation of non-binding molecular orbitals, which can be identified in the Mulliken population analysis as increased occupation of U atom's 5f orbitals, similar to the case of bond lengthening in UF 6 À [46]. The same configurations are maintained on bilayer graphene and are shown in Fig.…”