Photoelectron spectra of polynuclear aromatics. III. The effect of nonplanarity in sterically overcrowded aromatic hydrocarbons

Abstract

Articles you may be interested inPhotoelectron spectra of polynuclear aromatics. V. Correlations with ultraviolet absorption spectra in the catacondensed seriesThe high-resolution photoelectron spectra of 65 polycyclic aromatic hydrocarbons containing up to II condensed benzene rings have been obtained in the gas phase at temperatures between 20 and 450"C. Vibrational analysis of the spectra coupled with semiempirical MO calculations permitted positive identification of the 71' ionizations in the 6-11 eV range. Irrespective of size and symmetry of the hydrocarbons, two-thirds of all 71' bands are found to precede the onset of (T ionization, which occurs at 1O.6±0.2 eV in the molecules beyond naphthalene. The possibility of lahn-Teller forces operating in the degenerate ionic ground states of D 3h and D 6h molecules is discussed, and comments are made on the origin of the 1350 cm -\ vibrational progression that prevails in the first band of all planar hydrocarbons. In sterically overcrowded systems, excitation of low-frequency twisting and out-of-plane bending modes results in a blurring of the vibrational structure. In cases where reliable x-ray data are unavailable (e.g., dibiphenylene-ethylene), this observation allows a distinction to be made between planar and nonplanar hydrocarbons. The present data are of sufficiently high quality to permit the question as to the planarity of phenanthrene to be settled with some certainty. 12 14 FIG. 4. The photoelectron spectrum of peropyrene (286°).

Vibrational and Electronic Spectroscopy of Acenaphthylene and Its Cation

“…Despite the apparent coincidence between the 0.80-eV band in the electronic absorption spectrum and the 0.77-eV peak (relative to the 8.22 eV fundamental) in the photoelectron spectrum, 49 we consider them to be different transitions. We assign the former to the transition to the lowest ( 2 A 2 ) excited state while the latter is ascribed to the transition to the second lowest ( 2 B 2 ) excited state.…”

“…The lowering of the symmetrical mode frequencies in the excited state compared to the ground state has been observed previously for the fluorene radical. 53 The low intensity absorption band observed at 469 nm (2.74 eV), 49 Unlike the acenaphthylene radical cation, the geometry difference between neutral and cation does not significantly affect the excitation energies of acenaphthene radical cation at the B3LYP/6-31G(d,p) optimized neutral geometry, the BLYP/ 6-31G(d,p) transition energies fall at 1.02 ( 2 B 2 ), 2.06 ( 2 B 2 ), 2.70 ( 2 A 2 ), and 2.88 ( 2 A 1 ) eV. They agree with the observed photoelectron peak positions of 0.98, 1.94, 2.7, and 2.9 eV (all relative to the fundamental at 7.82 eV).…”

Ambient pressure photoelectron spectroscopy: A new tool for surface science and nanotechnology

“…A school of instrumentation evolved around the study gaseous organic molecules [4] using He I and He II excitation sources. Since no windows were used in these instruments the sample pressure was about equal to that of the gas discharge [5] , which ranged up to several mbar.…”

On the Carrier of the Extended Red Emission and Blue Luminescence

“…For example, the work function of pentacene is 5.15 eV (Fukagawa et al 2006), and the ionization energy of pentacene molecule is 6.74 eV (Boschi et al 1974). In comparison, we obtained 5.3 eV for the work function of the filmy-QCC by UV photoelectron spectroscopy with He i.…”