Auger decay of molecular double core-hole state

Abstract

1We report on theoretical Auger electron kinetic energy distribution originated from sequential two-step Auger decays of molecular double core-hole (DCH) state, using CH 4 , NH 3 and H 2 CO molecules as representative examples. For CH 4 and NH 3 molecules, the DCH state has an empty 1s inner-shell orbital and its Auger spectrum has two well separated components. One is originated from the 1st Auger transition from the DCH state to the triply ionized states with one core hole and two valence holes (CVV states) and the other is originated from the 2nd Auger transition from the CVV states to quadruply valence ionized (VVVV) states. Our result on the NH 3Auger spectrum is consistent with the experimental spectrum of the DCH Auger decay observed recently [Phys. Rev. Lett. 105, 213005 (2010)]. In contrast to CH 4 and NH 3 molecules, H 2 CO has four different DCH states with C1s −2 , O1s −2 and C1s −1 O1s −1 (singlet and triplet) configurations, and its Auger spectrum has more complicated structure compared to the Auger spectra of CH 4 and NH 3 molecules.In the H 2 CO Auger spectra, the C1s −1 O1s −1 DCH → CVV Auger spectrum and the CVV → VVVV Auger spectrum overlap each other, which suggests that isolation of these Auger components may be difficult in experiment. The C1s −2 and O1s −2 DCH → CVV Auger components are separated from the other components in the H 2 CO Auger spectra, and can be observed in experiment. Two-dimensionalAuger spectrum, representing a probability of finding two Auger electrons at specific pair of energies, may be obtained by four-electron coincidence detection technique in experiment. Our calculation shows that this two-dimensional spectrum is useful in understanding contributions of CVV and VVVV states to the Auger decay of molecular DCH states.

N1s and O1s double ionization of the NO and N2O molecules

“…However, only the features at 350 eV and 420 eV can be ascribed to Auger transitions, while the structure at higher energies is apparently due to accidental coincidences involving scattered electrons present in the spectrometer and, most likely, electrons from the O1s −1 normal Auger process. The present calculations and those made previously for NH 3 , 12 both predict kinetic energies around 350 eV and 420 eV for Auger electrons from N1s −2 states. The spectrum calculated in the present study, and shown along with the experimental data in Fig.…”

“…The two-electron integrals involving the Auger electron orbital were approximated using the population of MOs. 12,20 Further details of the calculation procedure are described in Ref. 12.…”

“…This observation is in qualitative agreement with previous studies, where double core hole electron spectra are found to exhibit much larger chemical shifts than single ionization spectra. [3][4][5][6][7][8][9][10][11][12] The ratio between the double and single ionization energies is for both the terminal and central nitrogen atoms 2.20, the same as obtained for the NO In the corresponding coincidence map (not shown), the double core hole states are represented by two straight lines, which intersect the horizontal and vertical axes at 203.1 and 193.5 eV, respectively. In addition to these two lines, a faint line is found which intersects the axes at about 180 eV.…”

“…To provide theoretical evidence for the interpretation of these Auger spectra CASSCF (complete active space self-consistent field) and CASCI (complete active space configuration interaction) calculations were performed of the Auger kinetic energies and intensities using a theoretical procedure similar to the one described previously for calculations of the corresponding Auger spectra for CH 4 , NH 3 , and H 2 CO. 12 …”

“…[3][4][5][6][7][8][9][10][11][12]. Double core hole (DCH) electron spectra may therefore provide improved chemical information, especially concerning close lying states.…”