The Band 12 Issue in the Electron Momentum Spectra of Norbornane: A Comparison with Additional Green's Function Calculations and Ultraviolet Photoemission Measurements

Abstract

In continuation of a recent study of the electronic structure of norbornane [J. Chem. Phys., 2004, 121, 10525] by means of electron momentum spectroscopy (EMS), we present Green's Function calculations of the ionization spectrum of this compound at the ADC(3) level using basis sets of varying quality, along with accurate evaluations at the CCSD(T) level of the vertical (26.5 eV) and adiabatic (22.1 eV) double ionization thresholds under C(2v) symmetry. The obtained results are compared with newly recorded ultraviolet photoemission spectra (UPS), up to binding energies of 40 eV. The theoretical predictions are entirely consistent with experiment and indicate that, in a vertical depiction of ionization, shake-up states at binding energies larger than approximately 26.5 eV tend to decay via emission of a second electron in the continuum. A band of s-type symmetry that has been previously seen at approximately 25 eV in the electron impact ionization spectra of norbornane is entirely missing in the UPS measurements and theoretical ADC(3) spectra. With regard to these results and to the time scales characterizing electron-electron interactions in EMS (10(-17) s) as compared with that (10(-13) s) of photon-electron interactions in UPS, and considering the p-type symmetry of the electron momentum distributions for the nearest 1b(1) and 1b(2) orbitals, this additional band can certainly not be due to adiabatic double ionization processes starting from the ground electronic state of norbornane, or to exceptionally strong vibronic coupling interactions between cationic states derived from ionization of the latter orbitals. It is therefore tentatively ascribed to autoionization processes via electronically excited and possibly dissociating states.

Theoretical study of molecular vibrations in electron momentum spectroscopy experiments on furan: An analytical versus a molecular dynamical approach

“…[40][41][42] Further physical phenomena that can strongly influence the recorded momentum distributions pertain to nuclear dynamics. Following Hajgató et al 43 or Deleuze et al, 44,45 it is useful to distinguish nuclear dynamics in the initial and neutral electronic ground state, comprising thermally induced conformational rearrangements [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] or pseudo-rotational motions, 61,62 from nuclear dynamics in the final ionized state, more specifically, geometrical relaxation, vibronic coupling interactions, and ultra-fast bond cleavages [43][44][45][63][64][65][66][67] induced by the ionization processes of interest.…”

Green's function study of the one‐electron and shake‐up ionization spectra of unsaturated hydrocarbon cage compounds

“…A vertical depiction of ionization is therefore expected to prevail for EMS. 50 At last, we wish to stress that, although they account for ground state correlation in the wavefunction of the neutrals, KS orbitals provide only empirical insights into the angular dependence of (e, 2e) ionization intensities. For quantitatively interpreting EMS measurements, we therefore strongly advocate ADC(3) calculations of ionization spectra and of (e, 2e) spherically averaged electron momentum distributions using 87,91 the related Dyson orbitals.…”

“…49,50 Extremely impressive differences around the vertical double ionization threshold have been observed between photon-and electron-impact measurements of the electronic structure of the latter molecule, 50 which suggests that the sudden removal of two electrons in fully saturated cages may therefore induce ultra-fast molecular dissociation processes 51 and complicated nuclear dynamic effects 52 in the ionization spectra. In continuation to the work described in refs.…”

Simulation of Photoelectron Spectra Using the Reflection Principle in Combination with Unrestricted Excitation ADC(2) to Assess the Accuracy of Excited‐State Calculations

“…[70] Within IP-ADC(3) the one-hole (1h) and two-hole-one-particle (2h1p) ionization potentials were computed consistently through third-and first-order perturbation theory according to the famous Møller-Plesset partitioning of the Hamiltonian. This resulted in accuracies of~0.2 [65,67,71] and~0.6 eV [72] for the 1h and 2h1p states, respectively, employing a basis set approaching completeness. The spectra were calculated up to binding energies of 26 eV, retaining all eigenvalues of the IP-ADC(3) secular matrix with a pole strength equal to or larger than 0.005.…”