Photodissociation spectroscopy of Mg+–rare gas complexes

Abstract

Weakly bound complexes of the form Mg+–RG (RG=Ar, Kr, Xe) are prepared in a pulsed nozzle/laser vaporization cluster source and studied with mass-selected photodissociation spectroscopy. The chromophore giving rise to the molecular spectra in these complexes is the 2P←2S Mg+ atomic resonance line. A 2Σ+ ground state and 2Σ+ and 2Π excited states are derived from this atomic transition. Vibrationally resolved spectra are measured for each of these complexes in the A 2Π←X 2Σ+ electronic transition. These systems are redshifted from the atomic resonance line, indicating that each complex is more strongly bound in its excited 2Π state than it is in the ground state. Extended vibrational progressions allow determination of the respective vibrational constants: Mg+–Ar, ωe′ = 272 cm−1; Mg+–Kr, ωe′ = 258 cm−1; Mg+–Xe, ωe′ = 258 cm−1. Extrapolation of the excited state vibrational progressions, and combination with the known atomic asymptotes and spectral shifts, leads to determination of the respective dissociation energies: Mg+–Ar, D0″= 1281 cm−1 (3.66 kcal/mol; 0.159 eV); Mg+–Kr, D0″ = 1923 cm−1 (5.50 kcal/mol; 0.238 eV); Mg+–Xe, D0″ = 4182 cm−1 (11.96 kcal/mol; 0.519 eV). The spin–orbit splitting in the 2Π1/2,3/2 state for all complexes is larger than expected by comparison to the Mg+ atomic value. This larger splitting in the complexes, which is attributed to configuration mixing with states on the rare gas atoms, increases for the series Ar, Kr, Xe, and decreases linearly for higher vibrational states of each complex.