Asymmetric lineshapes associated with predissociating levels of NO(E2Σ+)

Abstract

Two-colour multiphoton optical–optical double-resonance techniques have been used to study the spectroscopy and photophysics of the E²Σ⁺(σ²π⁴4sσ¹) Rydberg state of nitric oxide. The ν= 3 vibrational level is observed to be predissociated, with an efficiency that is very sensitive to the rotational quantum state. The results substantiate previous proposals that the heavily predissociated I²Σ⁺_{ν= 4} valence level acts as a ‘doorway’ state in the radiationless transfer from E_{ν= 3} to the A′²Σ⁺ continuum and ground-state atomic products. They also provide rare illustrations of the dissociative perturbation of a discrete molecular level by a ‘continuum of finite bandwidth’. In accord with theoretical expectation, transitions to certain of the more heavily predissociated rotational levels of E_{ν= 3} are observed to show markedly asymmetric lineshapes.