Resonance-enhanced multiphoton ionisation spectroscopy of jet-cooled bis(η6-benzene)chromium

The molecules of bis(η6-benzene)chromium cooled in a supersonic jet are ionised efficiently by nanosecond pulses of a tuneable dye laser operating in the region of the 3dz2→R4px,y Rydberg transition (26 600–27 100 cm−1). The mass spectra reveal a surprisingly strong signal from the intact molecular ions. The yield of the molecular ions increases in a two-colour experiment. The resonance-enhanced multiphoton ionisation (REMPI) spectra reveal two vibronic components of the Rydberg transition at 26 754 and 27 017 cm−1. The distance between these peaks (263 cm−1) corresponds to the frequency of the symmetric metal–benzene stretch in the Rydberg state.