Photodissociation spectroscopy of the Mg⁺-CO₂ complex and its isotopic analogs

Mg⁺-CO₂ ion-molecule cluster complexes are produced by laser vaporization in a pulsed nozzle cluster source. The vibronic spectroscopy in these complexes is studied with mass-selected photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer. Two excited electronic states are observed (2) ²Σ⁺ and ²Π. The ²Π state has a vibrational progression in the metal-CO₂ stretching mode (ω′_e=381.8 cm^-1). The complexes are linear (Mg⁺-OCO) and are bound by the charge-quadrupole interaction. The dissociation energy (D″ ₀) is 14.7 kcal/mol. Corresponding spectra are measured for each of the 24, 25, and 26 isotopes of magnesium. These results are compared to theoretical predictions made by Bauschlicher and co-workers.