Laser induced emission spectra of polyyne molecules C2nH2 (n = 5–8)

New optical emission spectra of linear carbon molecules, polyynes C2nH2 (n = 5–8), were observed upon UV-laser excitation of the 0–0 band of the dipole-allowed transition, 1 Σ u + ← X 1 Σ g + , of size-separated polyyne molecules in hexane. The emission spectra of C10H2 showed distinct peaks at 436 and 480 nm with a separation of ∼2100 cm−1 for a stretching vibration of the sp-carbon chain. Weak absorption features were also recorded in near-UV regions in shorter wavelengths to compare with the emission spectra. The spectral features in the emission were assigned to the vibronic bands of the forbidden electronic transition, 1 Δ u → X 1 Σ g + .