Results
of an exhaustive experimental study
of the valence electronic structure
of thiophene using high resolutionelectron momentum spectroscopy at impact energies
of 1200 and 2400 eV are presented. The measurementswere performed using an electron momentum spectrometer
of the third generation at
Tsinghua University,which enables energy, polar and azimuthal angular resolutions
of the order
of E = 0.8 eV,
= ±0.53
and
= ±0.84
. These measurements were interpreted by comparison with Green's function calculations
of one-electron and shake-up ionization energies as well as
of the related Dyson orbital electron momentumdistributions, using the so-called third-order algebraic diagrammatic construction scheme (ADC(3)). Comparison
of spherically averaged theoretical electron momentum distributions with experimental results very convincinglyconfirms the presence
of two rather intense
-2 *
+1 shake-up lines at electron binding energies
of 13.8 and15.5 eV, with pole strengths equal to 0.18 and 0.13, respectively. Analysis
of the electron momentumdistributions associated with the two lowest
2A
2 (
3-1) and
2B
1 (
2-1) cationic states provides indirect evidencefor a symmetry lowering and nuclear dynamical effects due to vibronic coupling interactions between thesetwo states. ADC(3) Dyson orbital momentum distributions are systematically compared with distributionsderived from Kohn-Sham (B3LYP) orbitals, and found to provide most generally superior insights intoexperiment.