Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi. It is argued that because of the high density of electronic states at the ground separated atom limit in these molecules, the predissociation threshold in each case corresponds to the thermochemical bond dissociation energy. The resulting bond dissociation energies are D(TiSi) = 2.201(3) eV, D(ZrSi) = 2.950(3) eV, D(HfSi) = 2.871(3) eV, D(VSi) = 2.234(3) eV, D(NbSi) = 3.080(3) eV, and D(TaSi) = 2.999(3) eV. The enthalpies of formation were also calculated as ΔH°(TiSi(g)) = 705(19) kJ mol, ΔH°(ZrSi(g)) = 770(12) kJ mol, ΔH°(HfSi(g)) = 787(10) kJ mol, ΔH°(VSi(g)) = 743(11) kJ mol, ΔH°(NbSi(g)) = 879(11) kJ mol, and ΔH°(TaSi(g)) = 938(8) kJ mol. Using thermochemical cycles, ionization energies of IE(TiSi) = 6.49(17) eV and IE(VSi) = 6.61(15) eV and bond dissociation energies of the ZrSi and NbSi anions, D(Zr-Si) ≤ 3.149(15) eV, D(Zr-Si) ≤ 4.108(20) eV, D(Nb-Si) ≤ 3.525(31) eV, and D(Nb-Si) ≤ 4.017(39) eV, have also been obtained. Calculations on the possible low-lying electronic states of each species are also reported.

The ionization energy (IE) of NdO and the low-energy electronic states of NdO+ have been examined by means of two-color photoionization spectroscopy. The value obtained for the IE, 5.5083(2) eV, is 0.54 eV higher than previous estimates. This leads to the conclusion that the autoionization reaction Nd + O → NdO+ + e− is exothermic by 1.76(10) eV. Thirty vibronic levels of NdO+ arising from eight electronic states were observed with partial rotational resolution. The energy level pattern and supporting electronic structure calculations indicated that all of the observed states correlated with the Nd3+(4f3, 4I)O2− configuration. The structure was consistent with a ligand field theory model where the electronic states of the Nd3+(4f3, 4I) atomic ion define a repeated motif in the electronic state energy intervals of the molecular ion. Comparisons with UO+ show close similarity in the electronic structures of these isoelectronic species.

The low-energy electronic states of UN and UN+ have been examined using high-level electronic structure calculations and two-color photoionization techniques. The experimental measurements provided an accurate ionization energy for UN (IE = 50 802 ± 5 cm−1). Spectra for UN+ yielded ro-vibrational constants and established that the ground state has the electronic angular momentum projection Ω = 4. Ab initio calculations were carried out using the spin–orbit state interacting approach with the complete active space second-order perturbation theory method. A series of correlation consistent basis sets were used in conjunction with small-core relativistic pseudopotentials on U to extrapolate to the complete basis set limits. The results for UN correctly obtained an Ω = 3.5 ground state and demonstrated a high density of configurationally related excited states with closely similar ro-vibrational constants. Similar results were obtained for UN+, with reduced complexity owing to the smaller number of outer-shell electrons. The calculated IE for UN was in excellent agreement with the measured value. Improved values for the dissociation energies of UN and UN+, as well as their heats of formation, were obtained using the Feller–Peterson–Dixon composite thermochemistry method, including corrections up through coupled cluster singles, doubles, triples and quadruples. An analysis of the ab initio results from the perspective of the ligand field theory shows that the patterns of electronic states for both UN and UN+ can be understood in terms of the underlying energy level structure of the atomic metal ion.

LiBe has been the subject of several theoretical investigations and one spectroscopic study. Initially, these efforts were motivated by interest in the intermetallic bond. More recent work has explored the potential for producing LiBe and LiBe + at ultracold temperatures. In the present study, we have advanced the spectroscopic characterization of several electronic states of LiBe and the ground state of LiBe + . For the neutral molecule, the 1 2 Π, 2 2 Σ + , 3 2 Σ + , and 4 2 Π(3d) states were observed for the first time. Data for the 2 2 Σ + −X 2 Σ + transition support a theoretical prediction that this band system is suitable for direct laser cooling. Photoelectron spectroscopy has been used to determine the ionization energy of LiBe and map the low-energy vibrational levels of LiBe + X 1 Σ + . Overall, the results validate the predictions of high-level quantum chemistry calculations for both LiBe and LiBe + .

Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe. It is argued that the sharp onset of predissociation corresponds to the bond dissociation energy in each of these molecules due to their high density of states as the ground separated atom limit is approached. The bond dissociation energies obtained are D(TiSe) = 3.998(6) eV, D(ZrSe) = 4.902(3) eV, D(HfSe) = 5.154(4) eV, D(VSe) = 3.884(3) eV, D(NbSe) = 4.834(3) eV, and D(TaSe) = 4.705(3) eV. Using these dissociation energies, the enthalpies of formation were found to be ΔH(TiSe(g)) = 320.6 ± 16.8 kJ mol, ΔH(ZrSe(g)) = 371.1 ± 8.5 kJ mol, ΔH(HfSe(g)) = 356.1 ± 6.5 kJ mol, ΔH(VSe(g)) = 372.9 ± 8.1 kJ mol, ΔH(NbSe(g)) = 498.9 ± 8.1 kJ mol, and ΔH(TaSe(g)) = 562.9 ± 1.5 kJ mol. Comparisons are made to previous work, when available. Also reported are calculated ground state electronic configurations and terms, dipole moments, vibrational frequencies, bond lengths, and bond dissociation energies for each molecule. A strong correlation of the measured bond dissociation energy with the radial expectation value, ⟨r⟩nd, for the metal atom is found.