High-Resolution Photoelectron Spectroscopy of the X⁺ ²Σ⁺ Ground State of CaAr⁺

The structure of the X+ 2Σ+(v+) ground state of CaAr+ was characterized by pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy. The spectra were recorded from the CaAr metastable a 3Π0-(v″ = 0) state using a resonance-enhanced (1 + 1') two-photon excitation scheme via the intermediate Ca(4s5s)Ar 3Σ+ (v' ≤ 9) state. The adiabatic ionization energy of the metastable a3Π0- state of CaAr, corresponding to the CaAr+ X+ 2Σ+ (v+ = 0, N+ = 0) ← CaAr a 3Π0- (v″ = 0, J″ = 0) ionization threshold, was determined to be EI/(hc) = 33432.86(20) cm-1. Vibrational levels of the X+ 2Σ+ ground electronic state of CaAr+ in the range v+ = 0 - 15 have been characterized with partial resolution of the rotational structure, allowing an accurate determination of the potential-energy function which takes into account long-range interactions. The dissociation energy and equilibrium bond length of the X+ 2Σ+ ground state of CaAr+ were determined to be De = 845(4) cm-1 (D0 = 810(4) cm-1) and Re = 2.990(3) Å, respectively.