A study of the electronic structures of Pd−2 and Pd2 by photoelectron spectroscopy

Abstract

The ultraviolet negative ion photoelectron spectrum of Pd−2 is presented for electron binding energies up to 3.35 eV. The anion is prepared by sputtering in a flowing afterglow ion source. Multiple low-lying electronic states of Pd2, all unidentified previously, are observed with resolved vibrational structure. The spectrum shows two strong electronic bands, each with similar vibrational progressions. Franck–Condon analyses are carried out on the two transitions and molecular constants are extracted for the anion and the two neutral electronic states. With the help of simple molecular orbital arguments and ab initio calculations, these two electronic bands are assigned as the triplet ground state (3Σ+u) and a singlet excited state (1Σ+u). The adiabatic electron affinity is E.A.(Pd2)=1.685±0.008 eV and the singlet excitation energy T0(1Σ+u) is 0.497±0.008 eV (4008±65 cm−1 ). The bonding in the palladium dimers is discussed and we find that the anion bond strength is 1.123±0.013 eV stronger than that of the neutral. Related studies of Pd− yield an improved electron affinity of E.A.(Pd)=0.562±0.005 eV.

Structural properties of nanoclusters: Energetic, thermodynamic, and kinetic effects

“…On the other hand, Watari and Ohnishi (1998) found that the CO is more stable than the Ih at N = 13 by density-functional calculations. Moseler et al (2001) were able to compare their results about vertical electron detachment energies for anionic clusters with the experimental data (Ervin et al, 1988;Ganteför and Eberhardt, 1996;Ho et al, 1991) obtaining a good agreement. At larger sizes, ab initio results are few, being restricted to the comparison of a small set of selected structures at some special sizes.…”

Theoretical studies of Pd metal deposition on the √3×√3 4-mercaptopyridine self-assembled monolayer

“…This means that a Pd 2 molecule coordinated between 4MP molecules binds approximately 3 times as strong as a Pd 2 dimer in vacuum, D e = 1.03 ± 0.16 eV [39]. This strong binding in gas phase (i.e., without considering the solvent) might possibly stabilize a vertical diffusion pathway for the Pd dimer, effectively promote permeation of Pd through the SAM, which is expected under non-electrochemical conditions.…”

Chemisorption of benzene on metal dimer anions: A study by photoelectron detachment spectroscopy

“…The calculated force constant indicates a typical covalent bond strength of the intermetallic bond in Pt 2 ͑C 6 H 6 ). 25,26 The ground state spectroscopic constants of Pt 2 ͑C 6 H 6 ) Ϫ and Pt 2 ͑C 6 H 6 ) are very similar to those of Pt 2 Ϫ and Pt 2 , respectively ͑Table I͒. The harmonic potential curves as deduced from the spectroscopic parameters are shown in Fig.…”

“…The hybridization of the d-orbitals of palladium with the frontier orbitals of benzene is evident from the enhanced photoelectron intensity above 2 eV where the transitions within the d-orbital region are predicted for palladium. 21,25 The photodetachment spectrum of Pd 2 Ϫ ͑Ref. 25͒ shows only a weak photoemission intensity in this binding energy region, which is explained by the small photoemission cross sections of the d-orbitals.…”

“…These small vibrational energies are characteristic for a Pd-Pd stretch vibration; e.g., the ground state vibrational energy of Pd 2 is 26 meV. 25,26 The only slightly modified vibrational energy serves as evidence that the palladium dimer is free to vibrate along its intermetallic bond. This suggests that the benzene is bound to Pd 2 in a similar configuration to that of Pt 2 ͑C 6 H 6 ).…”