Shape-Resonance-Enhanced Nuclear-Motion Effects in Molecular Photoionization

In this paper, we use a combination of photoelectron spectroscopy, mass spectrometry, and density functional theory calculations to get a detailed understanding of valence single and double ionization and the subsequent dissociation processes. This is exemplified on benchmark systems, trimetallo-dodecacarbonyls M 3 (CO) 12 with M = Ru, Os, where the energy remaining in the molecule after photoionization can be retrieved by measuring the degree of fragmentation of the molecular ion. The intensity of different mass peaks can thus be directly related to ionization cross sections obtained by photoelectron spectroscopy. We find that the M-CO dissociation energy rises as the number of CO ligands decreases due to dissociation. Moreover, ionization of the CO ligands has a higher cross section than that of the metal center for both single and double ionization. After advanced fragmentation, a CO bond can break and the carbon atom remains bonded to the metal core. In addition, we found that the valence ionization cross sections of M 3 (CO) 12 are maximal at about 40 eV photon energy thus showing a more pronounced shape resonance than Ru and Os-complexes with a single metal atom center. Finally, an np → nd giant resonance absorption causes a significant increase of the ionization cross section above 50 eV for Ru 3 (CO) 12 . C 2015 AIP Publishing LLC. [http://dx

Section: A Photon Energy Dependence Of the Electron Spectramentioning

confidence: 86%

Ionization and photofragmentation of Ru3(CO)12 and Os3(CO)12

Schalk

Josefsson

Richter

et al. 2015

“…Thus, it possible to compare the rotational substructure between the two bands as a function of incident photon energy, analogous to a previous study on vibrationalrotational-electronic ͑V-R-E͒ correlations in 2 u Ϫ1 photoionization of N 2 . 37 It is well known that the effects of shape resonances are influenced by the bond length for diatomic systems, 69,70 so it is reasonable to inquire if the rotational substructure would be affected, particularly in the lower energy region where the shape resonant effects are dominant. This comparison has been generated, and the results are shown in Fig.…”

Section: A Typical Comentioning

confidence: 99%

Rotationally resolved photoionization: Influence of the 4σ→kσ shape resonance on CO+(B 2Σ+) rotational distributions

Farquar

Miller

Poliakoff

et al. 2001

We present experimental and theoretical results on rotational distributions of CO ϩ (B 2 ⌺ ϩ ) photoions. Rotational distributions were determined for both the v ϩ ϭ0 and v ϩ ϭ1 vibrational levels following photoionization of cold (T 0 Ϸ9 K) neutral CO target molecules. Data were generated using dispersed ionic fluorescence over a wide range of photoelectron kinetic energies, 0рE k р120 eV, which allows one to interrogate the ionization dynamics. This wide spectral coverage permits illustrative comparisons with theory, and calculated spectra are presented to interpret the data. In particular, the comparison between theory and experiment serves to identify the strong continuum resonant enhancement at h exc Ϸ35 eV in the lϭ3 partial wave of the 4→k ionization channel, as this feature has profound effects on the ion rotational distributions over a wide range of energy. Second, there are differences between the rotational substructure for the v ϩ ϭ0 and v ϩ ϭ1 vibrational levels. All of the experimentally observed features and trends are reproduced by theory, and the consequences of these comparisons are discussed.

“…39 In the case of neutral diatomic molecules, dramatic changes in the PAD have been observed between different vibronic photoionization bands of N 2 , CO, and O 2 . [40][41][42] Such effects are associated with strong coupling of the electronic and vibrational motion and usually a breakdown of the Born-Oppenheimer approximation as a consequence of excitation of intermediate, autoionizing Rydberg states or shape resonances. 42 It is well known that the PAD is dependent on electron kinetic energy ͑E͒.…”

Section: Introductionmentioning

confidence: 99%

“…[40][41][42] Such effects are associated with strong coupling of the electronic and vibrational motion and usually a breakdown of the Born-Oppenheimer approximation as a consequence of excitation of intermediate, autoionizing Rydberg states or shape resonances. 42 It is well known that the PAD is dependent on electron kinetic energy ͑E͒. 43 To separate the effect of vibrational excitation from the E dependence, one must, ideally, compare transitions that terminate in different vibrational states but correspond to the same E. This approach requires experiments at multiple, carefully selected photoexcitation wavelengths.…”

Section: Introductionmentioning

confidence: 99%

Vibronic coupling in the superoxide anion: The vibrational dependence of the photoelectron angular distribution

Duzor

Mbaiwa

Wei

et al. 2010

The ZCC model invokes vibrational channel specific "detachment orbitals" and attributes this behavior to coupling of the electronic and nuclear motion in the parent anion. The spatial extent of the model detachment orbital is dependent on the final state of O 2 : the higher the neutral vibrational excitation, the larger the electron binding energy. Although vibronic coupling is ignored in most theoretical treatments of PADs in the direct photodetachment of molecular anions, the present findings clearly show that it can be important. These results represent a benchmark data set for a relatively simple system, upon which to base rigorous tests of more sophisticated models.