Electronic spectrum of the protonated diacetylene cation (H2C4H+)

Abstract : TheHB1A1 HX1A1 electronic band system of the protonated diacetylene cation (H2C4H+) is measured over the 230–295 nm range by photodissociating H2C4H+ ions stored in a cryogenic ion trap and by photodissociating H2C4H+ tagged with Ar and N2 in a tandem mass spectrometer. The HB 1A1 HX1A1 band system has an origin at 34 941 cm1 for H2C4H+, 34 934 cm1 for H2C4H+–Ar, and 34 920 cm1 for H2C4H+–N2. The spectra of H2C4H+, H2C4H+–Ar, and H2C4H+–N2 display similar vibronic structure, which is assigned using ab initio calculations to progressions in two symmetric a1 C–C stretch vibrational modes (6 and 4), with band spacings of 860 and 1481 cm1, respectively.