Asymmetric lineshapes associated with predissociating levels of NO(E2Σ

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 Eν= 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 Eν= 3 are observed to show markedly asymmetric lineshapes.