Wavelength and Metal Dependence in the Photofragmentation of a Gas-Phase Lanthanide β-Diketonate Complex

Abstract

The time-of-flight mass spectra of tris(2,2,6,6-tetramethyl-3,5-heptanedionato) lanthanide(III) [or Ln(thd)3 with Ln = Eu, Tb, Gd] produced by laser-induced multiphoton ionization in a supersonic expansion were studied as a function of laser excitation wavelength. Resonance-enhanced multiphoton ionization (REMPI), monitoring the Eu(I) ion signal from gas-phase Eu(thd)3, was observed in three distinct visible-excitation regions, corresponding to electronic absorption transitions on neutral Eu(0) atoms. The confirmation of the presence of Eu(0) atoms in the beam supports the proposed mechanism for the production of Ln atoms through sequential dissociation of neutral thd ligands from the metal following photoexcitation into ligand-to-metal charge-transfer (LMCT) states. Evidence is also presented that the LnO+ and LnOH+ fragments observed in the mass spectrum are produced via a separate, competing fragmentation pathway. The branching ratios between the two fragmentation pathways are compared for Ln(thd)3 (Ln = Eu, Tb, Gd). The ligand-dissociation pathway that produces Ln atoms appears to be more favorable in Ln(thd)3 complexes with low-lying LMCT states. Finally, the observation of the Tb2(thd)6+ dimer and its associated fragmentation pattern, as well as the presence of metal carbides, which are relevant to carbon contamination in chemical vapor deposition, is discussed.

Effective photosensitized, electrosensitized, and mechanosensitized luminescence of lanthanide complexes

“…Using the photoreduction technique, we also observed the decomposition of Eu(III) complexes and the formation of Eu(II) compounds (EuO and EuS nanoparticles) under the condition of LMCT band excitation [63][64][65] . Decomposition processes using gas-phase and laser-assisted MOCVD techniques have also been reported 66,67 .…”

Photofragmentation Pathways for Gas-Phase Lanthanide Tris(isopropylcyclopentadienyl) Complexes

“…A weak signal for Ln­(iCp) + fragments is also observed in the mass spectra (vide infra). This suggests an intact ligand stripping reaction pathway of with neutral ligand-radical ejection, through laser excitation into the ligand-to-metal charge-transfer states, similar to the mechanism proposed for several other lanthanide complexes and as also illustrated in eq . − The binding energies for the three dissociation steps illustrated in eq are calculated as 3.8, 4.0, and 4.6 eV, respectively, for Ln = La.…”

“…There have been many studies on the photofragmentation pathways of gas-phase molecular compounds, − metal–organic complexes, − and clusters. , Recently, our group reported the unimolecular gas-phase photodissociation mechanisms of lanthanide tris­(η 5 -cyclopentadienyl) complexes, Ln­(Cp) 3 , and lanthanide tris­(tetramethylcyclopentadienyl) complexes, Ln­(TMCp) 3 , through both experimental photoionization time-of-flight mass spectrometry (PI-TOF-MS) and theoretical atomistic simulation of the fragmentation dynamics . It was hypothesized that two types of reaction pathways dominate in the photofragmentation of both Ln­(Cp) 3 and Ln­(TMCp) 3 precursors: intact ligand stripping, leading to the production of bare metal, and ligand cracking within the metal–ligand complex, giving rise to metal carbide and metal hydrocarbide compounds.…”

Advances in Deposition of Main‐Group Metal Oxides and Rare‐Earth Oxides from Metal Enolates

“…The dependence on wavelength and metal in the photofragmentation of [Ln(thd) 3 ] (Ln = Eu, Tb, Gd) was investigated 130 . The mechanisms of photodissociation and photoionization MOCVD from fluorinated precursors [Ln(dik) 3 ] (dik = hfac, fod) and [Ln(hfac) 3 (diglyme)] were studied by photoionization time-of-flight mass spectrometry.…”