Auger decay in the field of a positive charge

We consider the Auger decay of atomic inner-shell vacancies in the field of a positive charge, as it occurs in multiply ionized molecules and clusters in strong x-ray laser pulses. First-principles numerical calculations of the decay rate as a function of the ion-charge distance are presented for a series of Auger transitions. The dependence of the rate on the distance is analyzed qualitatively within the Wentzel theory. Our results show that Auger rates can be modified significantly at ion-charge distances of the order of chemical bond lengths. The origin of the predicted effect is traced back to the distortion of the valence orbitals by the field of the positive charge.

Figure 1

Schematic representation of one of the channels of the $1s$ Auger decay in Ne atom: an inner valence (2$s$) electron is filling the core vacancy, while an outer valence ($2p$) electron is ejected into continuum. The same final state results also from the $2p\to 1s$ recombination and $2s$ ionization (not shown here). The former (“direct”) and the latter (“exchange”) contributions interfere due to electron indistinguishability.

Figure 2

Auger decay width of ($2p_z^{-1}$) Mg${}^{+}$–H${}^{+}$ for Fano-ADC(2)x calculations as a function of the Mg-proton distance $R$ with $z$ the Mg-proton axis. Diamonds and solid line: atomic orbital basis centered both on Mg and on the proton; circles and long-dashed line: atomic orbital basis centered only on Mg; stars and short-dashed line: calculation for ($2p_z^{-1}$) Mg${}^{+}$ alone, with atomic orbital basis centered both on Mg and at the distance $R$ along the $z$ axis, showing the so-called basis set superposition error (BSSE); triangles and dashed-dotted line: atomic orbital basis centered on Mg only, with the $3s$ orbital of Mg being frozen at its shape at $R=6.5\AA$. The inset shows the low-$\Gamma$ part of the plot on logarithmic scale.

Figure 3

(a) Fano-ADC(2)x result for the Auger decay width of ($2p_z^{-1}$) Mg${}^{+}$–H${}^{+}$ as a function of the Mg-proton distance, $R$ (logarithmic scale); (b) $z$ expectation value of the Mg $3s$ orbital as a function of the Mg-proton distance, $R$, showing the extent of the orbital distortion along the Mg-proton axis; (c) mean radius of the Mg $3s$ orbital as a function of the Mg-proton distance, $R$, showing the spatial extent.

Figure 4

Decay width of ($2s^{-1}$) Mg${}^{+}$–H${}^{+}$ as a function of the Mg-proton distance, $R$. Diamonds and solid line: Fano-ADC(2)x calculation with atomic orbital basis centered both on Mg and on the proton; circles and long-dashed line: Fano-ADC(2)x calculation with atomic orbital basis centered only on Mg; stars and short-dashed line: BSSE (see Fig. 2); triangles and dashed-dotted line: Fano-ADC(2)x calculation with atomic orbital basis centered on Mg only, with the $3s$ orbital of Mg being frozen at its shape at $R=6.5\AA$.

Figure 5

Decay width of ($2p_z^{-1}$) Ar${}^{+}$–H${}^{+}$ as a function of the Ar-proton distance, $R$. Diamonds and solid line: Fano-ADC(2)x calculation with atomic orbital basis centered both on Ar and on the proton; circles and long-dashed line: Fano-ADC(2)x calculation with atomic orbital basis centered only on Ar; stars and short-dashed line: BSSE (see Fig. 2); triangles and dashed-dotted line: Fano-ADC(2)x calculation with atomic orbital basis centered on Ar only, with the $3p_z$ orbital of Ar being frozen at its shape at $R=6.5\AA$.