Vibronic analysis of the ion-pair (E0(+))<-ground state (X0(+)) transition of BrCl

Vibrationally and rotationally resolved spectra of the first-tier E0(+)(nu') ion-pair state <--X0(+)(nu '' =0) ground-state transition of jet-cooled BrCl near 145 nm were recorded by exciting the halogen with a tunable vacuum ultraviolet ''laser'' generated by four-wave difference mixing in Kr gas, and detecting the ions produced by (1+1') resonance enhanced multiphoton ionization in a linear time-of-flight mass spectrometer. J-numberings for thirty individual isotopic bands were established by ground-state combination differences, and per band rotational constants were derived. Extensive perturbations precluded the determination of an unambiguous absolute nu'-numbering for the observed features or equilibrium rotational constants. However, excited-state vibrational isotope shift measurements do indicate that transitions from nu ''=0 of the ground-state probe vibrational levels between nu ' = 173 and 205. (C) 1997 American Institute of Physics.