Neutral Lanthanum Research Articles

Ionization Energies and Ground-State Structures of Neutral Lan (n = 2–14) Clusters: A Combined Experimental and Theoretical Investigation

Neutral lanthanum clusters are studied by photoionization time-of-flight mass spectroscopy, laser threshold photoionization spectroscopy, and density functional theory (DFT). Mass abundance spectra (MS) registered at multiple photoionization wavelengths in the range of 195-230 nm by single photon ionization reveal the production of all sizes, Lan (n ≥ 50), in good abundance, nullifying previously predicted low abundances for certain sizes in the 3-14 size range. Also, the MS do not reveal the extraordinary stability of any specific size, as one would expect, from previous theoretical predictions of 7- and 13-atom clusters as magic. Ionization energies (IEs) are measured for Lan (n = 2-14) clusters. DFT has been used to determine the stable geometric isomers for 2- to 10-atom clusters and to calculate their IEs. The theoretical IEs of 2-7 atom clusters are in decent agreement with their experimental values; however, the theoretical IEs are somewhat lower by ∼0.4 eV for n ≥ 8 than their experimental IEs.

New odd-parity energy levels of the neutral lanthanum atom

The discovery of 22 new energy levels of the La atom, having odd parity, is reported. These levels were derived from an analysis of unclassified spectral lines found either in optogalvanic spectra and/or Fourier transform spectra. The reliability of results obtained from the combination principle of Ritz was verified by hyperfine structure investigations. Further three new odd-parity levels of the first La ion are found. For two already known odd-parity levels substantial changes, concerning total angular momentum and hyperfine structure constants A, must be made.

New even-parity energy levels of the neutral Lanthanum atom derived from difficult to interpret measurements

We report the discovery of seven even-parity energy levels of the Lanthanum atom. These levels are derived from experimental results which are quite difficult to interpret, since most of the investigated structures appear in complicated blend situations. 17 spectral lines can be classified as transitions in which these levels are involved.Further we could improve the J-values and hyperfine structure constants A of two earlier published levels due to the investigation of additional lines.

New Energy Levels of Neutral Lanthanum Derived from an Optogalvanic Spectrum between 5610 and 6110 Å

In a previous paper, we reported on a complete optogalvanic (OG) spectrum of a discharge burning in a La–Ar gas mixture, in the spectral range 5610–6110 Å (17,851 to 16,364 cm−1). Now we are able to communicate further new energy levels, found via searching for laser-induced fluorescence lines when exciting unclassified lines from the OG spectrum. We were able to find 17 new levels, and for two further levels, the line list has extended. With the help of these 19 levels, we could classify 132 spectral lines.

Accurate CI-MBPT calculation of radiative lifetimes and transition probabilities of neutral lanthanum (La I) odd states with J = 3/2

An accurate calculation of radiative lifetimes and transition probabilities of the first 21 odd states with a total angular momentum J = 3/2 was performed for La I using configuration-interaction many-body perturbation theory (CI-MBPT). A technique to obtain correct transition amplitudes was devised for pairs of states with substantial mixing that improved the theoretical accuracy. The results were compared to known experimental and theoretical data for the considered transitions. It has been shown that the transition data calculated with CI-MBPT and with corrections for pairs of mixed states are in good agreement with the latest experimental data of Den Hartog et al, 2015 J. Phys. B: At. Mol. Phys. 48, 155 001, better than other theoretical results. The transition data can find many applications in astrophysics, and the CI-MBPT formalism with mixing correction is applicable to other atoms similar to or more complex than La I.

The Optogalvanic Spectrum of Neutral Lanthanum between 5610 and 6110 Å

We report on a complete optogalvanic spectrum of a discharge burning in a La-Ar gas mixture, in the spectral range 5610–6110 Å (17,851 to 16,364 cm−1). About 1900 overlapping laser scans, each between 1 and 1.5 cm−1 wide, were necessary to cover this range. The resolution of the spectra is limited by the Doppler width of the spectral features to about 0.03 cm−1 (or ca. 0.01 Å) and is comparable with a Fourier-transform spectrum, but the sensitivity is much higher. Indeed, we could find more than 1800 lines, from which about 800 could be classified as transitions between known energy levels. The main focus of the investigations was to discover previously unknown energy levels by means of excitation of unclassified spectral features.

Radiative Transition Parameters in Atomic Lanthanum from Pseudo-Relativistic Hartree–Fock and Fully Relativistic Dirac–Hartree–Fock Calculations

Calculated radiative transition probabilities and oscillator strengths are reported for 392 lines of neutral lanthanum (La I) atom in the spectral range from the near ultraviolet to the mid infrared. They were obtained using two different theoretical methods based on the pseudo-relativistic Hartree–Fock (HFR) and the fully relativistic multiconfiguration Dirac–Hartree–Fock (MCDHF) approaches, both including the most important intravalence and core-valence electron correlations. The quality of these radiative parameters was assessed through detailed comparisons between the results obtained using different physical models and between our theoretical results and the experimental data, where available. Of the total number of La I lines listed in the present work, about 60% have gf- and gA-values determined for the first time.

Transformation of the ionic liquid [EMIM][B(CN)4] into anionic and neutral lanthanum tetracyanoborate coordination polymers by ionothermal reactions.

The lanthanum tetracyanoborate coordination polymers [EMIM] [LaNO3{B(CN)4}3(H2O)3] (EMIM = 1-ethyl-3-methylimidazolium) and [La(NO3)2[B(CN)4](H2O)4] mark first examples of Ln-tetracyanoborates that have been obtained in ionothermal syntheses without further solvents to influence e.g. viscosity. Thereby, the ionic liquid [EMIM][B(CN)4] is fully incorporated into product formation.

Radiative lifetimes and transition probabilities of neutral lanthanum

The radiative lifetimes of 72 odd-parity levels of neutral lanthanum are measured to ±5% accuracy using time-resolved laser-induced fluorescence on a slow atomic beam. The levels range in energy from 15031 to 32140 cm−1. Branching fraction measurements using Fourier-transform spectroscopy are attempted and completed for all of the 72 levels. The branching fractions, when combined with the radiative lifetimes, yield new transition probabilities for 315 lines of the first spectrum of lanthanum (La i ). This study is part of a larger body of work on the radiative properties of rare earth neutral atoms, and is motivated by research needs in lighting science and astrophysics.

Methane Activations by Lanthanum Oxide Clusters

Density functional theory and coupled cluster theory were employed to study the activations of CH4 by neutral lanthanum oxide clusters (LaO(OH), La2O3, La3O4(OH), La4O6, La6O9) as models for the La2O3 catalysts for the oxidative coupling of methane (OCM) reaction. The physisorption energies (ΔH298 K) of CH4 on the lanthanum oxide clusters were predicted to be −4 to −3 kcal/mol at the CCSD(T) level. CH4 is activated by hydrogen transfer to one of the O sites on the lanthanum oxide clusters, and the energy barriers (ΔE0 K) from the physisorption structures were calculated to be modest at ∼20 kcal/mol for La2O3 and ∼25 kcal/mol for the other clusters. This is accompanied by the formation of a La–CH3 bond, whose bond dissociation energy (ΔE0 K) was calculated to be 53 to 60 kcal/mol. CH4 chemisorption is slightly exothermic on LaO(OH) and La2O3, whereas it becomes increasingly endothermic for the larger lanthanum oxide clusters. The formation of the CH3 radical was predicted to be substantially endothermic, by ∼50 kcal/mol for LaO(OH) and La2O3 and 64 to 76 kcal/mol for La3O4(OH) and La4O6 (ΔH298 K). Calculations on the activation of CH4 by La6O9 with a higher coordination number for both the La and O sites than La4O6 yield an energy barrier slightly higher by <1 kcal/mol, suggesting that the effects of the coordination numbers on the reaction energetics are rather small. The energy barrier for hydrogen abstraction does not correlate well with the negative charge on the O site, and a linear relation between the energy barrier and the chemisorption energy was not found for all the lanthanum oxide clusters, which is attributed to the strong dependency of their correlation on the specific chemical environment of the reactive site. Cluster reaction energies, physisorption and chemisorption energies, energy barriers, and La–CH3 bond energies calculated at the DFT level with the B3LYP and PBE functionals were compared with those calculated at the CCSD(T) level showing that the B3LYP functional yields better cluster reaction energies, chemisorption energies, and energy barriers. Although the PBE functional yields better physisorption energies, the DFT results can deviate substantially from the CCSD(T) values. Although the O2– sites in these cluster models were predicted to be less reactive toward CH4 than the O– sites modeled by the nonstoichiometric La2O3.33(001) surface (Palmer, M. S. et al. J. Am. Chem. Soc. 2002, 124, 8452), they are more reactive than the O22– site modeled on the stoichiometric La2O3(001) surface, which suggests the relevance of the lattice oxygen sites on the La2O3 catalyst surfaces in the OCM reaction.

Magnesium ion distribution and defect concentrations of MgO-doped lanthanum silicate oxyapatite

The distribution of magnesium ions at the lanthanum and silicon sites in MgO-doped lanthanum silicate oxyapatite as well as the concentration of neutral lanthanum vacancies were determined using densities and chemical compositions of the doped samples. On the basis of the density data, it was found that magnesium ions are substituted at the silicon site as well as the lanthanum sites in the oxyapatite phase. Owing to the existence of neutral lanthanum vacancies, it was difficult to evaluate the number of the oxygen ions present, which are related to the oxygen ion conductivity of the compound, from the chemical compositions of the samples alone. Further, it was found that the fact that the total conductivity of MgO-doped lanthanum silicate oxyapatite depends on the MgO concentration as well as that of other defects could not be explained on the basis of conventional defect chemistry. • Defect concentration in MgO-doped lanthanum silicate oxyapatite • Defect concentrations are quantitatively evaluated from the material density. • Mg ions are substituted not only on La sites but also on Si site.

New energy levels and hyperfine structure measurements of neutral lanthanum by laser-induced fluorescence spectroscopy

This study is focused on the search for new energy levels and the classification of weak spectral lines by analysing hyperfine (hf) spectra. Laser-induced fluorescence spectroscopy as well as optogalvanic spectroscopy were applied to measure the hf structure of Lanthanum transitions. Free La atoms are produced and excited in a hollow-cathode discharge. Ninety-six spectral lines have been analysed in the spectral range from 430 to 742 nm using a tunable single-mode cw dye laser operating with different dyes. Ninety-four of these lines are new, which means they are not listed in commonly used wavelength tables. A classification program was used to classify these 94 lines. Eighteen new energy levels were discovered. They were confirmed by further laser excitation. Fifty-one other spectral lines were classified via their hf pattern and centre-of-gravity wavenumber from Fourier transform spectra in order to prove the new even energy levels. In addition, 31 spectral lines were observed and classified as fluorescence transitions from the excited upper levels. A total of 176 spectral lines could be classified in this work. Seventy-three magnetic dipole hf structure constants A for the upper energy levels of the transitions were determined and compared with references, if available. Twenty-three of these constants are measured for the first time (including the A constants for 18 new levels).

Radiative lifetimes of highly excited odd-parity levels of neutral lanthanum

New radiative lifetimes of 24 high-lying odd-parity levels of neutral lanthanum are reported using time-resolved laser-induced fluorescence (TR-LIF) spectroscopy. The investigated levels ranging from 34 213 to 40 910 cm-1 were excited from the ground or metastable states using one-photon excitation. La atoms are produced by laser ablation on a solid La sample. The lifetimes were evaluated from transient LIF signals detected with a fast detection system. The obtained lifetime results, generally with uncertainties less than ±7%, are in the range from 15.7 to 121 ns.

Radiative lifetime measurements in neutral lanthanum using time-resolved laser-induced fluorescence spectroscopy in supersonic free-jet

Radiative lifetimes for 63 odd-parity energy levels of neutral lanthanum, in the range 13,260–30,965 cm−1, have been measured using time-resolved laser-induced fluorescence technique in a supersonic free-jet produced by laser vaporization of lanthanum metal. To the best of our knowledge, lifetimes for 45 levels are reported for the first time. The present lifetimes, with a few exceptions, are found to be in good agreement with the previously reported data. Lifetime values reported in this work fall in the range 9.5 to 313 ns and are accurate to ±10%. The levels belong to the 5d6s6p, 4f6s2, 6s26p, 5d26p, and 4f5d6s electronic configurations.

Radiative lifetime measurements on odd-parity levels of La I by time-resolved laser spectroscopy

Radiative lifetimes have been reported for 32 odd-parity levels of neutral lanthanum using a time-resolved laser-induced fluorescence technique in an atomic beam produced by laser ablation. The energies of these levels are in the range of 23,874 to 37,982 cm−1. Among the measured results, to the best of our knowledge, 23 lifetimes are reported for the first time. These lifetime values obtained in this paper, generally with uncertainties less than ±10%, are in the range of 7.3 to 247 ns. These results are in good agreement with previously reported data within the experimental errors.

Transition energies of neutral and singly ionized lanthanum

We have calculated the transition energies (ionization potential, excitation energies, electron affinity) of neutral lanthanum (La I) and singly ionized lanthanum (La II). The calculations are based upon the multiconfiguration Hartree-Fock (MCHF) method within the framework of Breit-Pauli relativistic corrections. These energies are important for determination of physical and chemical properties for La I and La II. Results obtained have been compared with other works.

Nature of the near-IR band in the electronic absorption spectra of neutral bis(tetrapyrrole) rare earth(III) complexes: Time-dependent density functional theory calculations

The nature of the near-IR band in the electronic absorption spectra of bis(tetrapyrrole) rare earth(III) complexes Y(Pc)2 (1), La(Pc)2 (2), Y(Pc)(Por) (3), Y(Pc)[Pc(α-OCH3)4] (4), Y(Pc)[Pc(α-OCH3)8] (5), and Y(Pc)[Pc(β-OCH3)8] (6) was studied on the basis of time-dependent density functional theory (TD-DFT) calculations. The electronic dipole moment along the z-axis in the electronic transition of the near-IR band in all the studied neutral bis(tetrapyrrole) yttrium(III) and lanthanum(III) double-deckers is well explained on the basis of the composition analysis of the orbitals involved. The electronic transition in the near-IR band causes the reversion of the orbital orientation of one tetrapyrrole ring in both homoleptic and heteroleptic bis(tetrapyrrole) rare earth complexes and induces electron transfer from the tetrapyrrole ring with lower orbital energy to the other ring in the heteroleptic bis(tetrapyrrole) rare earth(III) complexes. The near-IR band can work as an ideal characteristic absorption band to reflect the π–π interaction between the two tetrapyrrole rings in bis(tetrapyrrole) rare earth(III) double-decker complexes because of its peculiar electronic transition nature. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Scandium, Yttrium, and Lanthanum Benzyl and Alkynyl Complexes with the N-(2-Pyrrolidin-1-ylethyl)-1,4-diazepan-6-amido Ligand: Synthesis, Characterization, and Z-Selective Catalytic Linear Dimerization of Phenylacetylenes

1,4,6-Trimethyl-N-(2-pyrrolidin-1-ylethyl)-1,4-diazepan-6-amine (HL) reacts with M(CH2Ph)3(THF)3 to give the dibenzyl complexes (L)M(CH2Ph)2 (M = Sc, 1; M = Y, 2; M = La, 3). Compounds 1, 2, and 3 can be converted to their corresponding cationic monobenzyl species [(L)M(CH2Ph)]+ (M = Sc, Y and La) by reaction with [PhNMe2H][B(C6F5)4]. Reaction of (L)Sc(CH2Ph)2 with 2 equiv of phenylacetylene affords the monomeric dialkynyl complex (L)Sc(C≡CPh)2 (4), while reactions of (L)M(CH2Ph)2 (M = Y and La) give the dimeric dialkynyl complexes [(L)M(C≡CPh)(μ-C≡CPh)]2 (M = Y, 5; M = La, 6). The neutral complexes (2, 3, 5, and 6) and the cationic monobenzyl species [(L)M(CH2Ph)]+ (M = Y and La) are catalysts for the Z-selective linear head-to-head dimerization of phenylacetylenes. The cationic yttrium and the neutral lanthanum systems are the most effective catalysts in the series. The related scandium species show poor activity and selectivity.

Energies and Lifetimes for Some Excited Levels in La I

We calculated relativistic energies and Lande factors for 5d6s, 5d6s, 5d, 5d6s7s, 4f6s6p, 5d6s6p, 5d6p, and 4f5d6s levels in neutral lanthanum (Z = 57). We also obtained electric dipole transition energies and lifetimes for some excited levels. The calculations are based upon the multiconfiguration Hartree–Fock method within the framework Breit–Pauli relativistic corrections. Moreover, the results obtained were compared with other calculations and experiments.

Electric dipole transitions for La I ( Z=57)

Wavelengths, weighted oscillator strengths and transition probabilities for electric dipole ( E1) transitions for some excited levels in neutral lanthanum (La I, Z=57) have been calculated using the multiconfiguration Hartree–Fock (MCHF) method within the framework of Breit–Pauli relativistic corrections. Results obtained have been compared with other calculations and experiments. A discussion of these calculations for La I in this study has also been given in view of the MCHF method.