A. E. Boguslavskiy

Gas phase electronic spectra of the linear carbon chains HC2n+1H (n=3-6,9)

The B 3Σu−←X 3Σg− transitions of HC13H and HC19H have been measured in the gas phase, exhibiting broad, Lorentzian shaped bands. More extensive A 3Σu−←X 3Σg− spectra have been observed for HC2n+1H (n=3–6) than before with many new vibronic bands identified. The spectra were obtained by means of a mass selective resonant two-color two-photon ionization technique coupled to a supersonic plasma source. The electronic structures of this series of molecules (n=2–9) in both the ground and excited states have been investigated using DFT, MP2, and state-averaged CASSCF theories. The three lowest dipole allowed electronic transition systems are A 3Σu−←X 3Σg−, B 3Σu−←X 3Σg−, and C 3Πu←X 3Σg−, located, for the smaller members of the series, in the visible, UV and VUV range, respectively. The A 3Σu−←X 3Σg− system is found to be of medium intensity and the B 3Σu−←X 3Σg− transition is predicted to be very strong. This is a result of configuration mixing in the excited states. The oscillator strength of the lowest energ...

Gas phase electronic spectra of the carbon chains C5, C6, C8, and C9.

Three electronic absorption systems for C5 at 511, 445, and 232 nm and one for C6, C8, and C9 centered at 228, 259, and 288 nm have been observed in the gas phase. The C5 chain was produced in both discharge and ablation sources and detected using resonant two-color two-photon ionization spectroscopy involving 10.5 eV photons. The decay of the excited singlet electronic states indicates fast intramolecular processes on a subpicosecond time scale. The internal energy is assumed to be trapped in a triplet state for at least 15 micros. Hole-burning experiments on the 2 (3)Sigma(u)- <-- X (3)Sigma(g)- transition of C6, C8, and (1)Sigma(u)+ <-- X (1)Sigma(g)+ of C9 confirm the predissociative nature of the excited electronic states.

Gas-phase electronic spectrum of the C14 ring

The electronic spectrum of a cyclic C(14) 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 C(14) based on time-dependent density-functional calculations and reactivity with H(2). The spectral pattern differs from that previously seen in the larger C(4n+2) member rings, C(18) and C(22), indicating some sort of a structural crossover.

The Electronic Spectra of Carbon Chains, Rings, and Ions of Astrophysical Interest

On the basis of a comparison of the electronic spectra of a number of carbon chains measured in the laboratory with diffuse interstellar band (DIB) absorptions, it is concluded that carbon chains and related systems comprising up to a handful of carbon atoms can not be the carriers, as originally suggested by Douglas. However, the detection of the weak absorptions in diffuse clouds due to C3 enables arguments to be brought forward why certain larger carbon chains remain viable candidates. Specifically the odd‐numbered carbon chains, C17, C19, … have special spectroscopic properties: their lowest electronic transitions lie in the 400–900 nm DIB range, as is known from observation in neon matrices, and manifest very large oscillator strengths. An attempt to measure these in the gas phase was unsuccessful, but the electronic spectrum of a bare C18 ring could be observed. Particularly striking is the similarity of its origin band profile at temperatures in the 20–100 K range with some DIB measurements at high...