Vacuum ultraviolet-visible double resonance spectroscopy of NO. Observation of the high excited ns and nd Rydberg series

The two-color double resonance multiphoton ionization and fluorescence dip spectra due to the transitions from various rotational levels of the D ²Σ⁺ ( v = 1 ) state of NO to its high Rydberg states have been measured. Coherent vacuum ultraviolet (VUV) light generated by four wave mixing in Hg was used in the first excitation step. The ns(v = 1 ) and nd(v = 1 ) Rydberg series with 7 ≤ n ≤ 32 were observed. The rotational analysis for the d Rydberg series indicates that only the Pi;^- component appears in the MPI spectra. A large dependence of the rotational constant upon n for the nd Π^- Rydberg states was found and interpreted in terms of dΠ^--dΔ^- mixing. An anomalous intensity distribution was also found for the rotational branches of the ns Rydberg states in the transition from the D ²Σ ⁺ state. The anomaly is explained by the ns-(n -1 )d mixing.