Characterization of the first excited 1Π1 and the ground X 1Σ+ states of MgXe. I. Analysis of the 1Π1←X 1Σ+ bound–bound transitions

Abstract

Laser induced fluorescence (LIF) excitation spectra recorded for the vibrational bands in the Mg(3s3p 1P1)⋅Xe(1Π1)←Mg(3s3s 1S0)⋅Xe (X 1Σ+) system have been analyzed, yielding absolute vibrational assignments and values of ωexe=1.585±0.02 and ωe=97.5±1.0 cm−1 for the 1Π1 state of 24Mg132Xe. From a Birge–Sponer extrapolation, the well depth of this state is estimated to be 1500 cm−1. Simulations of rotationally structured spectra of three of the most intense vibrational bands are consistent with R″e=4.56±0.12 Å for the X 1Σ+ state. From Morse function extrapolation of the excited state rotational constants from the simulations, and Franck–Condon intensity simulations of the 1Π1←X 1Σ+ vibrational progressions, R′e for the 1Π1 state is estimated to be 3.07±0.10 Å. The 1Π1 state of MgXe fluoresces strongly. The corresponding 1Π1 states of ZnXe and CdXe do not fluoresce, but ‘‘action’’ spectra from the production (via predissociation) of metal atom 3PJ states are observed. Possible reasons for these differences are discussed in terms of spin–orbit induced predissociation. It is concluded that predissociation of the MgXe(1Π1) state is not observed because the crossing between the repulsive 3∑+1 and the attractive 1Π1 potential curves does not occur until energies higher than those accessible experimentally. Possible reasons for the behavior of the diatomic MgXe(1Π1) state vs that of Mg(3s3p 1P1) isolated in solid Xe, where production of Mg(3s3p 3PJ) states competes with Mg(3s3p 1P1) fluorescence, are also discussed. Finally, the attractive ‘‘bonding’’ interactions in the MgXe(1Π1) state are analyzed in terms of electrostatic interactions and compared with those for other Π-type states of metal/rare-gas van der Waals diatomic molecules.