Determination of the K—LL Auger Spectra of N2, O2, CO, NO, H2O, and CO2

Abstract

A double-focusing electrostatic electron spectrometer has been used to measure the K—LL Auger spectra resulting from electron impact for each of the elements in the gaseous molecules N2, O2, CO, NO, H2O, and CO2. An energy resolution of 0.09% full width half-maximum was normally employed. A method for analyzing these complex spectra is described. It involves the identification of normal and satellite lines. The former are defined as arising from single electron ionization from the K shell without additional excitation followed by an Auger process in which one electron fills the vacancy while a second goes into the continuum, and where all the other electrons remain in their same orbitals. Satellite lines result when extra excitation occurs either in the initial formation of the K vacancy or in the subsequent Auger process. To aid in the identification of these satellite lines, auxiliary experiments have been performed such as the study of discrete energy losses in photoionization due to electron shake-up, and the comparison of Auger spectra produced by monoenergetic x rays. As a consequence of the analyses of the Auger spectra, information has been obtained on (1) the nature of initial excitation processes such as the transition of a K electron into excited discrete states and monopole excitation and (2) the identification of the energy and nature of the ground and excited states of the doubly charged molecular ions. The second ionization potential was obtained for each of the molecules, and in one case, N2, the third ionization potential was estimated. Finally, a brief discussion is made of the possible use of high resolution electron spectroscopy in molecular as well as elemental analysis.

Auger Electron Emission from Fixed-in-Space CO

“…The electronic ground state and the two first excited states are indicated by solid lines. The figure confirms earlier findings [2,6,[14][15][16] that the narrow peak in the Auger spectrum at around 250.5 eV results from a decay to the second 1 Σ + potential curve (see the correlation diagram Fig. 2) which then couples to the first 3 Σ − curve leading to the ionic ground states.…”

“…One of the challenges results from the number and complexity of the final states. The many very broad overlapping structures in the Auger energy distribution often do not allow for a clear assignment of the decay channel [2]. A second challenge results from the interaction of the Auger electron with the molecular potential.…”

Triple ionization of CO2 by valence and inner shell photoionization

“…The creation of CO + 2 ions with vacancies in the C1s or O1s shells produces vibrational excitation in the molecule 1 and is followed within a few femtoseconds (fs) by Auger decay. Single (non-resonant) Auger decay from singly charged inner shell ionized states has been studied extensively [2][3][4][5] and produces doubly charged species; the same species have also been examined at higher resolution by coincidence methods applied to valence shell photoionization. 6,7 Some of the doubly charged species are stable CO ++ 2 molecules, while others dissociate into singly and doubly charged fragments.…”

Auger Electron Angular Distribution of Double Core-Hole States in the Molecular Reference Frame

“…2 ) formed by shake-off ionization [27,28] also appear in this range, 348-355 eV, along with satellites of the main Auger feature. Figure 3 shows the rich AES of isotropic N 2 along with a third generation synchrotron reference spectrum from Ref.…”