Abstract The emission spectra of the radical cations of tricetylene, Ã 2Π g→X̃ 2Π u band system, and of tetraacetylene, Ã 2Π u→X̃ 2Π g O o o band, excited in the gaseous phase by controlled electron impact, are reported. The emission spectrum of diacetylene cation, Ã 2Π u→X̃ 2Π g band system, with corrected band intensities is also presented. The lifetimes of the lowest vibrational level of the Ã 2Π excited states have been measured as 71±3 ns, 17±2 ns and ⩽6 ns for the cations of diacetylene, triacetylene and tetraacetylene respectively. The lifetimes of the measured excited vibronic levels are shorter. Emission bands from the radical cation of cyanoacetylene and cyanogen were however not detected and these results are discussed.