Jet-resolved vibronic structure in the higher excited states of N2O: Ultraviolet three-photon absorption spectroscopy from 80 000 to 90 000 cm−1

Abstract

Ionization-detected ultraviolet multiphoton absorption spectroscopy reveals Rydberg structure in the excited states of N2O within 20 000 cm−1 of the first ionization threshold. This structure persists, with atomic-like quantum defects and vibrational structure well matched with that of the ion, despite evidence for coupling of vibrationally excited Rydberg states with the underlying valence continuum. In the most completely resolved spectrum, which is assigned to the 3pσ 1Π state, hot-band, fundamental and overtone transitions involving the bending mode ν2, indicate Renner–Teller and Herzberg–Teller coupling of electronic and vibrational angular momentum. Vibronic intensities and positions suggest that these couplings can be regarded as properties of the N2O+ ion core, mirroring behavior manifested in the electronic emission spectrum of the ion. Window resonances are observed in the ionization-detected absorption spectrum above the four-photon ionization threshold, which are assigned to vibrationally excited Rydberg states that couple to competing continuua in which predissociation dominates Δv=−1 vibrational autoionization.