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- Cheng, Xiao, et al.
(författare)
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Vibrationally-Resolved X-ray Photoelectron Spectra of Six Polycyclic Aromatic Hydrocarbons from First-Principles Simulations
- 2022
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 126:33, s. 5582-5593
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Tidskriftsartikel (refereegranskat)abstract
- Vibrationally resolved C 1s X-ray photoelectron spectra (XPS) of a series of six polycyclic aromatic hydrocarbons (PAHs; phenanthrene, coronene, naphthalene, anthracene, tetracene, and pentacene) were computed by combining the full core hole density functional theory and the Franck–Condon simulations with the inclusion of the Duschinsky rotation effect. Simulated spectra of phenanthrene, coronene, and naphthalene agree well with experiments both in core binding energies (BEs) and profiles, which validate the accuracy of our predictions for the rest molecules with no high-resolution experiments. We found that three types of carbons i (inner C), p (peripheral C bonded to three C atoms), and h (peripheral C bonded to an H atom) show decreasing BEs. In linear PAHs (the latter four), h-type carbons further split into h1 or h2 (on inner or edge benzene ring) subtypes with chemical shifts of ca. 0.2–0.4 eV. All major Franck–Condon-active modes are characterized to be in-plane vibrations: low-frequency (<800 cm–1) C–C ring deformation modes play an essential role in determining the peak asymmetries; and for each h-type carbon a high-frequency (ca. 3600 cm–1) C*–H stretching mode is responsible for the high-energy tail. We found that core ionization leads to reduction of all C*–C and C*–H bond lengths and ring deformation with a definite direction. Based on theoretical spectra of four linear PAHs, we found asymptotic relations and anticipated possible spectral features for even larger linear PAHs. Our calculations provide accurate reference spectra for XPS characterizations of PAHs, which are useful in understanding the vibronic coupling effects in this family.
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- Wei, Minrui, et al.
(författare)
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Vibronic fine structure in the nitrogen 1s photoelectron spectra of molecules from Franck-Condon simulations: Azines
- 2022
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 106:2
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Tidskriftsartikel (refereegranskat)abstract
- Vibronic coupling plays a pivotal role in molecular spectroscopy. We present a theoretical study on vibrationally resolved x-ray photoelectron spectra (XPS) of seven azines (CxHyNz; pyridine, three diazines, two triazines, and one tetrazine) at the nitrogen 1s edge, to explore the vibronic coupling effects as influenced by consecutive replacement of the CH group with a N atom. Franck-Condon simulations were performed with the Duschinsky rotation effect included, where the electronic structure was calculated by the density functional theory. Validations on pyrimidine show good agreement with the experiment, weak functional dependence, and weak mode mixing effect. We observed an evident blue shift in binding energies with the increasing number of N atoms in this series, together with molecule-dependent vibronic fine structures. These molecules have either C2v or Cs molecular symmetry at the optimized core-ionized geometries. Franck-Condon-active vibrational modes were identified to be low frequency (500–1650 cm−1), totally symmetric (A1 or A′), in-plane ring deformation modes. Core ionization on N∗ always leads to elongation of the N∗−N bond length, accompanied by an increase of the ∠C−N∗−X bond angle (X=C, N). Our study predicts accurate theoretical reference spectra for the azine family and provides useful information on the properties of the core-ionized states as influenced by the structural change of CH↔N replacement.
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