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Characterization of the electronic ground state of Mg$_2^+$ by PFI-ZEKE photoelectron spectroscopy

The $\mathrm{X}^+\ ^2Σ_u^+$ ground electronic state of the Mg$_2^+$ ion has been studied by pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy. Rotationally cold Mg$_2$ molecules produced in a laser-ablation supersonic-expansion source were ionized by resonant two-photon absorption from the $\mathrm{X}\ ^1Σ_g^+(v"=0)$ ground vibronic state. The photoelectron spectra of the $v^+=3-14$ vibrational levels of the $\mathrm{X}^+$ state were recorded with rotational resolution and their analysis led to the determination of accurate term values and rotational constants for these levels. Improved values of the adiabatic ionization energy of $^{24}$Mg$_2$ ($51\,503.9(4)$ cm$^{-1}$) and of the ground-state dissociation energy of $^{24}$Mg$_2^+$ ($10 572.3(6)$ cm$^{-1}$) were determined from experimental data.