The Auger spectroscopy of pyrimidine and halogen-substituted pyrimidines

Abstract

The C 1s and N 1s Auger spectra of pyrimidine, 2-chloropyrimidine, and 5-bromopyrimidine have been measured in an electron impact experiment at 1000 eV. In the case of the halogen-substituted pyrimidines, also the Cl 2p and Br 3d Auger spectra have been recorded. We have thoroughly analyzed and interpreted all the Auger spectra recorded here with the aid of accurate Green's function calculations with a large basis set. The spectra are extremely complex with thousands of states contributing and almost no single-state feature even near the double ionization threshold. Besides reproducing and explaining with great detail nearly all the main spectral features observed, the calculations have successfully unraveled the interplay among the different C 1s core hole chemical shifts in each molecule and how this affects some fingerprinting details in the composite C 1s Auger spectra.

Resonant Auger spectroscopy at the carbon and nitrogen K-edges of pyrimidine

“…Therefore, the spectator RAE spectrum is expected to bear a close resemblance to the KVV Auger spectrum 19 shifted in energy by the screening effect of the spectator electron. The empirical procedure to use a shifted KVV Auger spectrum to interpret the RAE spectra J. Chem.…”

“…5,7,9 In the present case, the comparison has been guided by recent combined experimental and theoretical studies of the valence shell electronic structure by photoabsorption spectroscopy 30 and of the Auger spectrum of pyrimidine and halopyrimidines by electron impact. 19 The comparison between the N/C (1s) → π * RAE spectra and the corresponding N/C (1s) Auger electron spectra is reported in Figures 6(a) and 6(b), respectively. The Auger electron spectra are reported on their own double ionization (DIP) energy scale (top axis) obtained by subtraction of the electron kinetic energy from the binding energy of the inner-shell vacancy.…”

“…From this point of view the theoretical assignment of the C/N Auger electron spectra of Ref. 19 will be used as a guideline for the interpretation of the final states of the spectator RAE spectra. The socalled region-2 extending between 13 and 20 eV, is populated by an increasing number of mostly unresolved states, consisting of a mixture of 1h and eventually 2h1p configurations.…”

“…With such a shift it is clear that already in the region-2 the contribution of 2h1p states, populated by spectator transitions, is not negligible. Thus the theoretical assignment 19 of the N Auger electron spectrum can be used as a guideline for the interpretation of the final states in the RAE spectrum. The ADC(3) theoretical description of the N Auger electron spectrum of pyrimidine 19 assigns the first feature at 25.4 eV DIP to a 5b 2 −2 orbital, while a combination of the outermost four orbitals contribute to the second feature, at about 2.2 eV higher DIP.…”

“…Thus the theoretical assignment 19 of the N Auger electron spectrum can be used as a guideline for the interpretation of the final states in the RAE spectrum. The ADC(3) theoretical description of the N Auger electron spectrum of pyrimidine 19 assigns the first feature at 25.4 eV DIP to a 5b 2 −2 orbital, while a combination of the outermost four orbitals contribute to the second feature, at about 2.2 eV higher DIP. From Figure 6(a) it is clear that these two features contribute to the resonantly enhanced band of singly ionized states at about 14.4 and 16.7 eV, respectively, in the RAE spectrum.…”