Mass spectrometric investigation of gaseous YbH, YbO and YbOH molecules

Predissociation measurements of the bond dissociation energies of EuO, TmO, and YbO

The observation of a sharp predissociation threshold in the resonant two-photon ionization spectra of EuO, TmO, and YbO has been used to measure the bond dissociation energies of these species. The resulting values, D₀(EuO) = 4.922(3) eV, D₀(TmO) = 5.242(6) eV, and D₀(YbO) = 4.083(3) eV, are in good agreement with previous values but are much more precise. In addition, the ionization energy of TmO was measured by the observation of a threshold for one-color two-photon ionization of this species, resulting in IE(TmO) = 6.56(2) eV. The observation of a sharp predissociation threshold for EuO was initially surprising because the half-filled 4f⁷ subshell of Eu in its ground state generates fewer potential energy curves than in the other molecules we have studied by this method. The observation of a sharp predissociation threshold in YbO was even more surprising, given that the ground state of Yb is nondegenerate (4f¹⁴6s², ¹S_g) and the lowest excited state of Yb is over 2 eV higher in energy. It is suggested that these molecules possess a high density of electronic states at the energy of the ground separated atom limit because ion-pair states drop below the ground limit, providing a sufficient electronic state density to allow predissociation to set in at the thermochemical threshold.

Axion-mediated electron-electron interaction in ytterbium monohydroxide molecule

The YbOH triatomic molecule can be efficiently used to measure the electron electric dipole moment, which violates time-reversal (T) and spatial parity (P) symmetries of fundamental interactions [Kozyryev and Hutzler, Phys. Rev. Lett. 119, 133002 (2017)]. We study another mechanism of the T, P-violation in the YbOH molecule-the electron-electron interaction mediated by the low-mass axionlike particle. For this, we calculate the molecular constant that characterizes this interaction and use it to estimate the expected magnitude of the effect to be measured. It is shown that this molecular constant has the same order of magnitude as the corresponding molecular constant corresponding to the axion-mediated electron-nucleus interaction. According to our estimation, an experiment on YbOH will allow one to set updated laboratory constraints on the CP-violating electron-axion coupling constants.

Bond dissociation energies of low-valent lanthanide hydroxides: lower limits from ion-molecule reactions and comparisons with fluorides

Despite that bond dissociation energies (BDEs) are among the most fundamental and relevant chemical properties they remain poorly characterized for most elementary lanthanide hydroxides and halides. Lanthanide ions Ln+ = Eu+, Tm+ and Yb+ are here shown to react with H2O to yield hydroxides LnOH+. Under low-energy conditions such reactions must be exothermic, which implies a lower limit of 499 kJ mol-1 for the Ln+-OH BDEs. This limit is significantly higher than previously reported for YbOH+ and is unexpectedly similar to the BDE for Yb+-F. To explain this apparent anomaly, it is considered feasible that the inefficient hydrolysis reactions observed here in a quadrupole ion trap mass spectrometer may actually be endothermic. More definitive and broad-based evaluations and comparisons require additional and more reliable BDEs and ionization energies for key lanthanide molecules, and/or energies for ligand-exchange reactions like LnF + OH ↔ LnOH + F. The hydroxide results motivated an assessment of currently available lanthanide monohalide BDEs. Among several intriguing relationships is the distinctively higher BDE for neutral LuF versus cationic LuF+, though quantifying this comparison awaits a more accurate value for the anomalously high ionization energy of LuF.

A gas-inlet system coupled with a Knudsen cell mass spectrometer for high-temperature studies

A gas-inlet system coupled with a Knudsen effusion mass spectrometer has been developed to study at high temperature the interaction of solids and vapors with reactive permanent gases, such as H(2) and O(2), directly introduced into the cell from external low-pressure reservoirs (pressure range: 10(-4) < p < 1 bar). By selecting the gas flow from the external reservoir the pressures of the gases inside the Knudsen cell can be quantitatively controlled over three orders of magnitude, approximately from 10(-8) to 5.10(-5) bar. Mixtures of two different gases can be introduced into the cell, controlling their partial pressures independently. The capabilities of the device have been tested with four gas-solid systems: PbO(s) + O(2)(g), GeO(2)(s) + O(2)(g), Ga(s) + H(2)(g) and Au(s) + H(2)(g), by studying the relevant high-temperature equilibria. The results obtained for the dissociation energies of the diatomic molecules PbO(g), GeO(g), GaH(g), and AuH(g) compare well with the literature data giving confidence in the reliability and versatility of the method. Preliminary experiments on the in situ formation of H(2)O(g) in the Knudsen cell by the introduction of controlled gaseous H(2)/O(2) mixtures are also presented.