PHOTODISSOCIATION SPECTROSCOPY OF MG-GAS COMPLEXES( RARE)

Weakly bound complexes of the form Mg+-RG (RG=Ar, Kr, Xe) are prepared in a pulsed nozzle/ laser vaporization cluster source and studied wit h mass-selected photodissociation spectroscopy. The chromophore giving rise to the molecular spectra in these complexes is the (2)p<-S-2 Mg atomic resonance line. A (2) Sigma(+) ground state and (2) Sigma(+) a nd (II)-I-2 excited states are derived from this atomic transition. Vi brationally resolved spectra are measured for each of these complexes in the A (II)-I-2<-X (2) Sigma(+) electronic transition. These systems are redshifted from the atomic resonance line, indicating that each c omplex is more strongly bound in its excited (II)-I-2 state than it is in the ground state. Extended vibrational progressions allow determin ation of the respective vibrational constants: Mg+-Ar, w(') (e) = 272 cm(-1); Mg+-Kr, w(') (e) = 258 cm(-1); Mg+-Xe, w(') (e) = 258 cm(-1). Extrapolation of the excited state vibrational progressions, and combi nation with the known atomic asymptotes and spectral shifts, leads to determination of the respective dissociation energies: Mg+-Ar, D ''(O) = 1281 cm(-1) (3.66 kcal/mol; 0.159 eV); Mg+-Kr, D ''(O) = 1923 cm(-1 ) (5.50 kcal/mol; 0.238 eV); Mg+-Xe, D ''(O) = 4182 cm(-1) (11.96 kcal /mol; 0.519 eV). The spin-orbit splitting in the (II1/2,3/2)-I-2 state for all complexes is larger than expected by comparison to the Mg+ at omic value: This larger splitting in the complexes, which is attribute d to configuration mixing with states on the rare gas atoms, increases for the series Ar, Kr, Xe, and decreases linearly for higher vibratio nal states of each complex.