Electronic spectra of mass-selected HCH-Ar ( = 1-3) and HCH-(N) ( = 1-2) complexes are measured over the 290-530 nm range using resonance-enhanced photodissociation spectroscopy in a tandem mass spectrometer. Vibronic transitions in the visible region are compared with previous experimental and theoretical results for the ÃΠ ← X̃Π band system of HCH. Hole burning experiments confirm that transitions over the 290-340 nm range involve the diacetylene cation (HCH). On the basis of previous experiments and comparison with spectra of isoelectronic molecules the peaks are assigned to the 2Π ← X̃Π band system, with the origin transition for HCH-Ar occurring at 29723 cm. The main progression has a spacing of 906 cm and is assigned to the symmetric C-C stretch vibrational mode (ν). The assignment of additional bands is complicated by spectral congestion, the possible presence of energetically close-lying electronic states, vibronic coupling effects, and by the fact that HCH possibly becomes nonlinear in the 2Π state.
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