Variable-Energy Photoelectron Spectroscopy of Substituted Rhenium and Manganese Pentacarbonyls:  Molecular Orbital Assignments and the Interatomic Resonant Effect

Abstract

High-resolution variable-energy photoelectron spectra of M(CO)5X [M = Re, X = Re(CO)5, Cl, Br, and I; and M = Mn, X = Mn(CO)5 and Br] are reported. Tunable synchrotron radiation is used to distinguish the Re 5d and Br 4p orbital based peaks for the controversial Re(CO)5Br. Our results provide firm molecular orbital assignments for all of these molecules. The valence orbital in the ordering of ionization energies for M(CO)5Cl (M = Mn and Re) and Mn(CO)5Br is a 1(M-X) > e(X) > b2(M) > e(M); but for M(CO)5I (M = Mn and Re) and Re(CO)5Br the ordering is a1(M-X) > e(M) > b2(M) > e(X). The crossover of the HOMO in the Re molecules due to the change in the halogen electronegativities occurs at Re(CO)5Br. The metal np-->nd resonance is observed for all of these molecules. For molecules like M2(CO)10 (M = Re and Mn) and Mn(CO)5Br, the observation of this np-->nd resonance is useful in assigning the metal nd based orbitals in their valence level spectra. However, for molecules like Re(CO)5X (X = Br and Cl), a np-->nd type resonance is observed on bands arising from both Re 5d and halogen mp based orbitals. This new resonant effect on the ligand-based orbitals is shown to be mainly due to the interatomic resonant effect. The core and valence level chemical shifts of these compounds are treated using Jolly's approach to confirm the assignments for the valence level spectra of some of these molecules. The high-resolution inner valence and core level spectra of these compounds are reported. Broadening of Re 4f, Br 3d, and I 4d core level spectra is discussed. The Auger peaks are observed in the high-resolution, high-intensity Br 3d of Re(CO)5Br and I 4d of Re(CO)5I spectra.

Multiatom resonant photoemission

“…The microscopic theoretical model outlined here should also be capable of describing such corecore interatomic resonance effects in the intensities and angular distributions in photoemission from free molecules, 12 as well as with straightforward generalization the valencecore interatomic resonance effects mentioned previously. [8][9][10] Finally, we point out that the demonstrated importance of multiple scattering of soft x-ray radiation in the vicinity of strong core-level resonances should be of relevance in the analysis of resonant elastic and inelastic x-ray scattering, and other topics of high current interest. 35 …”

“…In addition, theoretical calculations based on the previously discussed microscopic model, 5 and on a simpler classical theory of x-ray optics 11 are presented and found to yield excellent agreement with the remaining experimental effects, thus clarifying the physics involved. We also comment on the implications of this work for other recent core-core and valence-core MARPE measurements, [6][7][8][9][10]12,13 as well as for x-ray emission 4,14 and x-ray scattering experiments.…”

“…1-4 Independent of this work on core-core multiatom resonant photoemission, other groups have reported the enhancement of valence photoemission intensities primarily associated with emission from a certain atom A upon tuning the photon energy through the core-level absorption edges of a nearby atom B, with this work including measurements near solid-solid interfaces 8,9 and on a free molecule. 10 No attempts have as yet been made to theoretically model this latter type of valence-core MARPE effect.…”

Observation and resonant x-ray optical interpretation of multi-atom resonant photoemission effects in O1semission from NiO

“…31,32,33,34 and discussed theoretically. 35,36,37 These effects have been observed experimentally in measurements near solid-solid interfaces (in which the interatomic effect occurs across the interface), 31,32 in emission from a molecular orbital in a free molecule, 33 and in valence emission from clusters of atoms.…”

“…31,32,33,34 and discussed theoretically. 35,36,37 These effects have been observed experimentally in measurements near solid-solid interfaces (in which the interatomic effect occurs across the interface), 31,32 in emission from a molecular orbital in a free molecule, 33 and in valence emission from clusters of atoms. 34 In the context of free molecules and atomic clusters, these effects have been termed interatomic coulomb decay (ICD), with a theoretical model having been elaborated 35 which is equivalent to that proposed previously for MARPE, but which considers also the interatomic Auger process, and for which the lower energies of excitation permit assuming that the wavelength of the exciting radiation is large with respect to the atomic distances involved.…”