Photodissociation spectroscopy of Mg +H 2O

Abstract

Mg +H 2O ion—molecule complexes are produced in a pulsed supersonic nozzle cluster source. These weakly bound complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as 2B 2→X 2A 1 is observed with an origin at 28399 cm −1 (vac). The spectrum has a prominent progression in the metal—H 2O stretching mode with a frequency (ω′ e) of 517.1 cm −1. An extrapolation of this progression fixes the excited state dissociation energy ( D′ 0) at 16008 cm −1. The corresponding ground state value ( D″ 0) is 8732 cm −1 (25.0 kcal/mol). The solvated bending mode and asymmetric stretching mode of water are also active in the complex. A second electronic transition assigned as 2B 1←X 2A 1 is observed with an origin at 30386 cm −1 and a metal stretch frequency of 483.4 cm −1. This study was guided by ab initio calculations by Bauschlicher and co-workers, which provide accurate predictions of the electronic transition energies, vibrational constants and dissociation energies.