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The Auger electron spectra (AES) following the chlorine 2p ionization in the gas phase alkali-chlorides as well as in the HCl and DCl molecules were studied theoretically and experimentally. Nonrelativistic ab initio calculations based on quantum chemical methods and the one-center approximation were used to compute the Cl L2,3VV AES. The vibrational band structure in the AES was simulated by full life time vibrational interference (LVI) theory and a more approximate moment method. Calculations were compared with the corresponding experimental electron or photon impact excited spectra. Overall features and changes in the series of the experimental AES are correctly predicted by the theory. For the most intense transitions in these spectra a qualitative explanation of the energies is given on the basis of a model that includes electrostatic interactions, Pauli repulsion, and polarization. This explains that the substantial changes of the spectra with X are due to a R−3 dependence of the electrostatic interaction on the X–Cl bond length. A comparison of the two theoretical methods shows that the LVI vibrational band breadths are well reproduced by the moment method in the AES of HCl, DCl, and LiCl, whereas the moment breadths are underestimated in the AES of NaCl and KCl. The LVI band breadths for HCl, DCl, and KCl are in good agreement with experimental data. In contrast, the experimental spectra for LiCl and NaCl show almost two times broader vibrational bands than predicted by the LVI theory. This contradiction indicates that the LiCl and NaCl vapors are contaminated by the dimer form of these substances. A large contribution of Li2Cl2 (74%) and Na2Cl2 (29%) was measured in the LiCl and NaCl vapors by time-of-flight mass spectroscopy. The Auger peaks in the spectra of the dimers lie very close to the monomer peaks, and thus make it very difficult to distinguish dimer and monomer contributions.

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The Cl(2p) photoelectron spectra of HCl and DCl have been measured with high resolution. Careful data analysis with a least-squares fitting method enabled us to determine the spectroscopic parameters for the three spin-orbit and molecular field split components of the Cl(2p) −1 states. The experimental results were compared with ab initio calculations. The values of 84 ± 9 meV, 71 ± 13 meV, and 103 ± 10 meV for the lifetime line widths of 2 1/2 , 2 + 1/2 , and 2 3/2 states were extracted from the experiment. An anomalous photoionization cross section ratio (60%) between the 2 + 1/2 and 2 3/2 states was observed.The chemical environment of an atom affects the ionization energies of valence and core orbitals. The recent progress in synchrotron radiation instrumentation and electron spectroscopy provides an opportunity to study the electronic structure of atoms and molecules in great detail. One of these details is the molecular field (MF) splitting in the binding energies of the core-ionized gas phase molecules. In crystals and solid state samples the MF splitting is commonly designated as the ligand field splitting. The core hole MF splitting effect is seen in cases where the core orbital has an atomic degeneracy, i.e. when the orbital angular momentum of the core orbital is greater than zero. The MF couples then with the spin-orbit (SO) interaction, which leads, e.g., in the Cl(2p) −1 configuration of the HCl molecule to three states: 2p −1 3/2,3/2 , 2p −1 3/2,1/2 , and 2p −1 1/2,1/2 . We will designate these here by the LS-coupling symbols ( 2 +1 ω ) : 2 3/2 , 2 + 1/2 , and 2 1/2 , respectively. The MF splitting in p and d core hole states has been extensively studied in recent years by several authors: see, e.g., [1][2][3][4][5][6][7][8].Recently, Gel'mukhanov et al [3] and Fink et al [9] predicted that the non-spherical electron distribution of a molecule causes an anisotropy on the Auger decay probabilities of the 2p core hole states of H 2 S and HCl. This finding was supported in a recent comparison [10] of the computed and experimental 2p photoabsorption profiles of HCl. The aim of the present study is to confirm the effect of the MF on the Cl(2p) total decay rates in HCl. This is done in a straightforward way by extracting the lifetime line widths from the photoelectron spectrum (PES).The measurements were performed at the beam line I411 of the MAX laboratory in Lund, Sweden. Synchrotron radiation for the beam line at the 1.5 GeV MAX II storage ring is generated by a hybrid undulator with 44.5 periods (89 poles