High-resolution spectroscopic study of the C 0+ and D 1 Rydberg states of KrXe and of the X 1/2 and A1 3/2 states of KrXe+

Abstract

The electronic spectrum of the C 0+, D 1←X 0+ transitions of KrXe has been studied at high resolution in the vicinity of the Kr(1S0)+Xe 6p[5/2]2 dissociation limit by resonance-enhanced (1+1′) two-photon ionization spectroscopy. The rotational structure of 13 bands, 5 and 8 of which correspond to transitions to levels of 0+ and 1 symmetry, respectively, were observed in the spectra of several isotopomers. The hyperfine structure in the spectrum of the Ω=1 levels of 84Kr129Xe was determined. The five transitions to levels of 0+ symmetry form a regular progression of bands characterized by a regular rotational structure and corresponding to high vibrational levels (with v=16–20) of the C 0+ state. The C 0+ state is found to possess significant X 1/2, A1 3/2 and A2 1/2 ion-core character in combination with an excited electron of 6pσ, 6pπ and 6sσ character, respectively, and to correlate adiabatically to the Kr(1S0)+Xe6s[1/2]1o dissociation limit. The transition to the eight levels of Ω=1 symmetry form a very irregular progression both as far as spectral positions and intensities are concerned. Rotational levels of f-symmetry, accessed via Q-branch transitions, are weakly predissociated by a repulsive level associated with the Kr(1S0)+Xe6s[1/2]0o limit. A local perturbation in the rotational structure of the fourth level of Ω=1 symmetry enabled the identification of a so far unobserved predissociative level of Ω=1 or Ω=2 symmetry with band center near 77318.5cm−1. The determination of the band centers, rotational constants and isotopic shifts of the Ω=1 levels led to the conclusion that the level structure is affected by homogeneous perturbations and that at least two electronic states of Ω=1 symmetry contribute to the spectrum of KrXe in this spectral region. Modelling the observed rovibronic structure using a coupling model involving low vibrational levels of a weakly bound Ω=1 state associated with the Kr(1S0)+Xe6s[1/2]1o dissociation limit and high vibrational levels of a more strongly bound state associated with the Kr(1S0)+Xe 6p[5/2]2 dissociation limit enabled us to reproduce the observed values of the rotational constants, vibronic positions and intensity distribution in a qualitatively satisfactory manner. However, the model failed to account for the observed isotopic shifts. Rotationally resolved photoelectron spectra of the KrXe+ X 1/2←KrXe C 0+ and KrXe+ A1 3/2←KrXe C 0+ ionizing transitions were recorded from selected rotational levels of selected isotopomers of KrXe. The rotational levels of the X 1/2 state of KrXe+ group as pairs of levels of opposite parity and have a spin-rotation coupling constant γ of approximately −2B, as a consequence of pure precession. The rotational level structure of the low-lying electronic states of KrXe+ thus appears to form the same patterns as the corresponding states of ArXe+.