Vibrationally resolved high-resolution NEXAFS and XPS spectra of phenanthrene and coronene

Abstract

We performed a combined experimental and theoretical study of the C1s Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectroscopy and X-ray Photoelectron Spectroscopy in the gas phase of two polycyclic aromatic hydrocarbons (phenanthrene and coronene), typically formed in combustion reactions. In the NEXAFS of both molecules, a double-peak structure appears in the C1s → LUMO region, which differ by less than 1 eV in transition energies. The vibronic coupling is found to play an important role in such systems. It leads to weakening of the lower-energy peak and strengthening of the higher-energy one because the 0 - n (n > 0) vibrational progressions of the lower-energy peak appear in nearly the same region of the higher-energy peak. Vibrationally resolved theoretical spectra computed within the Frank-Condon (FC) approximation and linear coupling model agree well with the high-resolution experimental results. We find that FC-active normal modes all correspond to in-plane vibrations.

Vibrationally resolved NEXAFS at C and N K-edges of pyridine, 2-fluoropyridine and 2,6-difluoropyridine: A combined experimental and theoretical assessment

“…The spectrum associated with the para C1s 1π * transition of pyridine has been chosen also as a test case to check the reliability of the VG model to describe vibronic effects. In fact, even if this model has been already used to simulate vibronic NEXAFS spectra, 45,14 a comparison with the results obtained with more refined vibronic models is, to the best of our knowledge, still lacking. For this purpose, the theoretical spectrum has been simulated also at the VH|FC level, therefore including mode-mixing effects.…”

Symmetry breaking and excitonic effects on optical properties of defective nanographenes

“…Indeed, smaller nanographene molecules, which might be known rather as polycyclic aromatic hydrocarbons (PAHs), have a long history of experimental and theoretical studies. 8,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] It is especially the case for those with odd-membered rings; PAHs with 5-membered rings are known as corannulene and those with 7-membered rings are 7-corannulene. Experimentally, their existence was confirmed and, theoretically, their atomic geometry and optical properties have been discussed in detail.…”

“…Experimentally, their existence was confirmed and, theoretically, their atomic geometry and optical properties have been discussed in detail. 14,18,19,21,[23][24][25][26][27][28] Although the PAHs have their defectless counterparts of almost the same size, the effect of the defect was not clarified through, for example, a comparative study. We consider that such a comparative study will be important in bridging the PAH chemistry and the nanographene chemistry.…”

The electronic characterization of biphenylene—Experimental and theoretical insights from core and valence level spectroscopy

“…For example, vibrational contributions could affect the spectra to spread various electronic contributions, minimizing the overlap between 1s and π*-orbitals 42 as well as deformations of the molecular structure 6 as they can occur during excitation processes.…”