Electronic absorption spectra of linear HC 2n+1 H + ͑n =2-7͒ were recorded in 6 K neon matrices following their mass-selective deposition. Four new electronic band systems are identified; the strongest Ẽ 2 ⌸ g/u ← X 2 ⌸ u/g lies in the UV and the second most intense C 2 ⌸ g/u ← X 2 ⌸ u/g is located in the visible range. The known à 2 ⌸ g/u ← X 2 ⌸ u/g absorption is an order of magnitude weaker than C 2 ⌸ g/u ← X 2 ⌸ u/g . Transitions to the B and D states are also discussed. The wavelengths of

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... he HC 2n+1 H + ͑n =2-7͒ electronic systems obey a linear relation as a function of the size of the cations, similar to other carbon chains. The B 3 ⌺ u − ← X 3 ⌺ g − transition in the UV of neutral HC 2n+1 H ͑n =4-7͒ has also been identified upon photobleaching of the cations trapped in the matrices.