Vibrationally resolved band profiles for autoionisation of NO (cΠ) nℓλ (vR=0) Rydberg states into NO AΠ (vi=0, 1, 2) vibronic levels

Excitation spectra for dispersed VUV-fluorescence of NO (λ_fl=134–152 nm) were measured in the exciting-photon energy range between 16.9 and 24.8 eV using monochromatised synchrotron radiation at medium bandwidth of 29 meV. Fluorescence from A¹Π (v_i=0, 1, 2) vibronic NO⁺-levels and fluorescence from excited dissociation fragments NI (3s ²P_J) was observed simultaneously by recording the dispersed fluorescence with a monochromator–position-sensitive detector combination. The autoionisation of NO (c³Π) nℓλ (v_R=0) Rydberg levels into the NO⁺ A¹Π (v_i=0, 1, 2) vibronic levels was observed vibrationally resolved. Different Beutler–Fano profiles for autoionisation of one Rydberg level NO (c³Π) nℓλ (v_R=0) into the different vibronic NO⁺ A¹Π (v_i=0, 1, 2) levels are clearly visible. The dependence of the Beutler–Fano profiles on the quantum numbers n, ℓ, and λ of the Rydberg electron is discussed. For the direct photoionisation into the NO⁺ A¹Π (v_i=0, 1, 2) vibronic levels a non-Franck–Condon behaviour was observed.