Vacuum ultraviolet laser/time-of-flight mass spectra of Xe2 near Xe (5d, 6p, 6s) atomic lines

Four Rydberg state <- ground-state transitions of supersonically cooled Xe2, in the vicinity of the Xe* (5d, 6p, 6sʹ) manifolds, have been excited with a tunable vacuum ultraviolet (VUV) "laser" generated by four-wave mixing in Kr or Hg nonlinear media. Molecular ions produced by (1 +1ʹ) resonance-enhanced multiphoton ionization (REMPI), and (or) atomic fragment ions resulting from excited-state predissociation followed by ionization, were mass selected in a linear time-of-flight (TOF) mass spectrometer. Vibrational analyses of two of the resultant spectra have led to excited-state molecular constants, while equilibrium bond lengths were estimated by Franck-Condon intensity simulations. Constants could be derived for a third transition but the REMPI/TOF spectra exhibit interesting intensity anomalies that prevented a bond length from being determined. The fourth system was found to be strongly perturbed. In the absence of rotational resolution, possible excited-state electronic symmetries were deduced from angular-momentum arguments. Possible reasons are presented for the observed distortions in the shapes of the Rydberg-state potential-energy curves from their expected nonbonding forms.