Multichannel quantum interference in the predissociation of Cs2: Observation of q-reversal in a complex resonance

State-specific photofragment yield spectrum is obtained in the 580 nm system of Cs2 by monitoring Cs (6 2P3/2). Strongly asymmetric line shapes are observed and interpreted as being due to resonances. We observed a gradual sign change of the Fano line shape parameter, which is called ‘‘q-reversal’’, for the first time in predissociation. Some of other lines show complex line shapes that cannot be fitted by a usual Beutler–Fano profile. These complex line shapes may be attributed to the interfering resonances.