Electron-Transfer-Mediated Decay and Interatomic Coulombic Decay from the Triply Ionized States in Argon Dimers

We report the first observation of electron-transfer-mediated decay (ETMD) and interatomic Coulombic decay (ICD) from the triply charged states with an inner-valence vacancy, using the Ar dimer as an example. These ETMD and ICD processes, which lead to fragmentation of ${\mathrm{Ar}}^{3+}\mathrm{\text{−}}\mathrm{Ar}$ into ${\mathrm{Ar}}^{2+}\mathrm{\text{−}}{\mathrm{Ar}}^{2+}$ and ${\mathrm{Ar}}^{3+}\mathrm{\text{−}}{\mathrm{Ar}}^{+}$, respectively, are unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ETMD or ICD electron and the kinetic energy release between the two fragment ions are measured in coincidence.

Figure 1

Schematic diagrams of (a) direct ICD (interatomic Coulombic decay), (b) exchange ICD, and (c) ETMD (electron-transfer-mediated decay).

Figure 2

Ar dimer ion-ion coincidence TOF spectrum.

Figure 3

(a) Relationship between the ICD electron energy and the total KER for the ${\mathrm{Ar}}^{3+}\mathrm{\text{−}}{\mathrm{Ar}}^{+}$ fragmentation of the argon dimer. (b) Kinetic energy distribution of the ICD electrons detected in coincidence with ${\mathrm{Ar}}^{3+}\mathrm{\text{−}}{\mathrm{Ar}}^{+}$ pairs.

Figure 4

Relationship between the ETMD electron energy and the total KER for the ${\mathrm{Ar}}^{2+}\mathrm{\text{−}}{\mathrm{Ar}}^{2+}$ fragmentation of the argon dimer. See the caption of Fig. 3 for the details.

Figure 5

Schematic energy diagram for the initial (labeled by 1–10) and final (labeled by $A\mathrm{\text{−}}C$ for ICD and $D\mathrm{\text{−}}I$ for ETMD) states of the interatomic processes. Initial states decay to final states which are energetically below them. 1, ${\mathrm{Ar}}^{3+}(3p^2({}^{1}D)4s{}^{2}D)\mathrm{\text{−}}\mathrm{Ar}$; 2, ${\mathrm{Ar}}^{3+}(3p^2({}^{3}P)4s{}^{2}P)\mathrm{\text{−}}\mathrm{Ar}$; 3, ${\mathrm{Ar}}^{3+}(3p^2({}^{3}P)4s{}^{4}P)\mathrm{\text{−}}\mathrm{Ar}$; 4, ${\mathrm{Ar}}^{3+}(3p^2({}^{1}D)3d{}^{2}D)\mathrm{\text{−}}\mathrm{Ar}$; 5, ${\mathrm{Ar}}^{3+}(3s3p^4{}^{2}P)\mathrm{\text{−}}\mathrm{Ar}$; 6, ${\mathrm{Ar}}^{3+}(3p^2({}^{3}P)3d{}^{4}P)\mathrm{\text{−}}\mathrm{Ar}$; 7, ${\mathrm{Ar}}^{3+}(3s3p^4{}^{2}S)\mathrm{\text{−}}\mathrm{Ar}$; 8, ${\mathrm{Ar}}^{3+}(3p^2({}^{3}P)3d{}^{2}P)\mathrm{\text{−}}\mathrm{Ar}$; 9, ${\mathrm{Ar}}^{3+}(3s3p^4{}^{2}D)\mathrm{\text{−}}\mathrm{Ar}$; 10, ${\mathrm{Ar}}^{3+}(3s3p^4{}^{4}P)\mathrm{\text{−}}\mathrm{Ar}$. A, ${\mathrm{Ar}}^{3+}(3p^3{}^{2}P)\mathrm{\text{−}}{\mathrm{Ar}}^{+}(3p^5{}^{2}P)$; B, ${\mathrm{Ar}}^{3+}(3p^3{}^{2}D)\mathrm{\text{−}}{\mathrm{Ar}}^{+}(3p^5{}^{2}P)$; C, ${\mathrm{Ar}}^{3+}(3p^3{}^{4}S)\mathrm{\text{−}}{\mathrm{Ar}}^{+}(3p^5{}^{2}P)$; D, ${\mathrm{Ar}}^{2+}(3p^4{}^{1}S)\mathrm{\text{−}}{\mathrm{Ar}}^{2+}(3p^4{}^{1}S)$; E, ${\mathrm{Ar}}^{2+}(3p^4{}^{1}D)\mathrm{\text{−}}{\mathrm{Ar}}^{2+}(3p^4{}^{1}S)$; F, ${\mathrm{Ar}}^{2+}(3p^4{}^{3}P)\mathrm{\text{−}}{\mathrm{Ar}}^{2+}(3p^4{}^{1}S)$; G, ${\mathrm{Ar}}^{2+}(3p^4{}^{1}D)\mathrm{\text{−}}{\mathrm{Ar}}^{2+}(3p^4{}^{1}D)$; H, ${\mathrm{Ar}}^{2+}(3p^4{}^{3}P)\mathrm{\text{−}}{\mathrm{Ar}}^{2+}(3p^4{}^{1}D)$; and I, ${\mathrm{Ar}}^{2+}(3p^4{}^{3}P)\mathrm{\text{−}}{\mathrm{Ar}}^{2+}(3p^4{}^{3}P)$. The vertical dashed line corresponds to the equilibrium bond length of the neutral Ar dimer 3.76 Å [24].