Femtosecond pump–probe photodissociation of OClO: direct observation of the 2A1 state and the role of accidental multiphoton resonance

Previous pump–probe experiments on the OClO molecule are analyzed and a consistent interpretation of the experimental observations is proposed. We demonstrate that a direct observation of the very weak 2A1 state of OClO is possible with a proper femtosecond pulse, and suggest that it is necessary to introduce an accidental resonance of the probe pulse with the highly excited D or E states for understanding the observed distinct photodissociation dynamics of the 2A2 state using pump pulses of slightly different wavelengths. A transient abnormal peak, observed in the OClO+ ion signal after a stronger excitation, is also convincingly interpreted.