In addition to infrared (IR) spectroscopy, electronic spectrum is an alternative method for detecting and determining the existence of a molecule . According to selection rules, the allowed transitions of sp-hybridized carbon chains are attributed to the 1 1 Σ u + ← X 1 Σ g + excitations. Here, we adopt two theoretical methods to calculate the excitation energies and oscillator strengths of the low-lying 50 excited states of the carbon chains H-(C≡C) n -H (n = 3-9, 15). Relevant data determined by TD-ωB97XD/def2-TZVP and the very robust while much more expensive STEOM-DLPNO-CCSD/def2-TZVP calculations as well as the available experimental values for the 1 1 Σ u + ← X 1 Σ g + transition are listed in Table . b This work, calculated at the STEOM-DLPNO-CCSD/def2-TZVP level.