Photodissociation spectroscopy of the Mg+–C2H2 π-complex

The Mg+–acetylene complex is produced by pulsed-nozzle laser vaporization and studied with mass-selected resonance-enhanced photodissociation spectroscopy. A progression of broad vibrational bands is observed near 347 nm. The broad linewidths, which preclude rotational resolution, are attributed to rapid predissociation in the excited state. The progression is assigned to the metal–acetylene stretch in the 2B1←X 2A1 band system, which produces vibrational constants of ωe′=330.5 cm−1 and D0′=13100 cm−1. The ground-state dissociation energy is estimated as D0″=6100 cm−1 (17.4 kcal mol−1). These properties are in good agreement with the predictions of theory.