Gas-phase electronic spectrum of the C₁₄ ring

The electronic spectrum of a cyclic C₁₄ in the visible range has been detected in the gas phase by a mass selective resonant two-color two-photon ionization technique coupled to a laser ablation source. Absorption is localized in the 19 000 to 20 000 cm⁻¹ region and appears as a dozen of 3–7 cm⁻¹ narrow peaks belonging to one or two close-lying electronic states. Bands have structures which for the narrowest ones is likely to be the rotational profile contour. The spectrum is attributed to a cyclic form of C₁₄ based on time-dependent density-functional calculations and reactivity with H₂. The spectral pattern differs from that previously seen in the larger C_4n+2 member rings, C₁₈ and C₂₂, indicating some sort of a structural crossover.