An Overlooked Series of Gas Phase Diatomic Metal Oxide Ions that Are Long-lived

Abstract

Although the "Golden" years of spectroscopy and the major studies on ionization processes now are behind us, as with many branches of science, much yet remains to be gleaned from such topics that is both full of interest and of significance to present day research. Presented here is one such overlooked example, an observation that relates to both these fields. An analysis is presented for the periodic table concerning the gas-phase thermochemical nature of MO+ and MO2+ ions. Unexpectedly, a pattern of 18 elements has been identified that exhibit the potential for having long-lived MO+ ions. Normally such molecular ions are expected to decay extremely rapidly by dissociative recombination with electrons, but in particular, 12 of this group behave not like molecules but rather as atomic ions. These are the diatomic oxide ions of Sc, Y, La, Zr, Hf, Ce, Pr, Nd, Pm, Gd, Tb, and Th. In the gas phase, they decay by much slower three-body recombination channels. As may be noted, these elements are located in the first two columns of the transition elements, among the earlier rare earths and an actinide. From all the elements, UO2+ is the only dioxide ion that behaves similarly. These findings now elevate the potential importance of these ions and should facilitate their spectral characterization. Moreover, subsequent comparisons with spectra of well-known isoelectronic and isovalent neutral monoxides and other diatomics will help in the stimulation of further theoretical advances. In addition, once characterized, an ease of spectrally monitoring such ionic states will provide a useful analytical tool.

The chemiionization reactions Ce + O and Ce + O2: Assignment of the observed chemielectron bands

“…The energy to dissociate CeO 2 + to Ce + and O 2 (X 3 Σ g − ) is 6.52 eV (spin‐free) and 6.28 eV (spin‐orbit), compared to the values of 6.39 eV (DC‐CCSD) and 6.77 eV (DC‐CCSD(T)). The experimental value is (5.7 ± 0.5) eV 46. The dissociation energy with respect to O 2 (a 1 Δ g ) computed at the CASPT2 level of theory is 7.48 eV which decreases to 7.24 eV upon including spin‐orbit effects.…”

“…The corresponding values with DC‐CCSD and DC‐CCSD(T) are 7.52 and 7.83 eV, respectively. The experimental value is (6.7 ± 0.5) eV 32, 46. On comparison with LaO, which has a closed‐shell ground state ( 1 Σ), CeO( 2 Σ) has the additional electron in a π bonding orbital.…”

Mass-analyzed threshold ionization spectroscopy of lanthanum-hydrocarbon radicals formed by C—H bond activation of propene

“…La is ionized by a single-photon ionization process as its IE (5.5769 eV) is lower than the laser energy used for recording the mass spectrum. 56 The IE of LaO has been reported as 4.95 (19) eV via a thermochemical analysis 57 or ≥5.19 eV by theoretical predictions. 58 Thus, LaO could be ionized via a single-photon ionization process as well.…”

Electronic structure of SmO and SmO− via slow photoelectron velocity-map imaging spectroscopy and spin-orbit CASPT2 calculations

“…The ionization energies of many of the lanthanide oxides (LnO) are smaller than their bond strengths. This results in the unusual situation of dissociative recombination of the cations with electrons, LnO + + e − → Ln + O (1) being endothermic. 1 Therefore, lanthanide oxide cations of this type should be long-lived in a weakly ionized plasma, a property generally only pertinent for atomic cations for which recombination must be slowly stabilized by radiative decay as opposed to the rapid dissociative stabilization 2 available to most polyatomics.…”