Electronic spectroscopy of carbon chains and relevance to astrophysics

Abstract

Laboratory measurements of electronic transitions in carbon chains are presented. Guided by the results found in neon matrices, gas-phase spectra have been obtained with two different experimental approaches. Electronic transitions of neutral carbon chains are detected in a supersonic slit jet plasma by cavity ring-down (CRD) spectroscopy, and those of mass-selected anions are probed by resonant two-colour electron photodetachment. The successful combination of matrix and gas-phase experiments is demonstrated for the examples of C₆H and C₁₄H^-. These, and other previous measure-ments on electronic transitions of long carbon chains in the gas phase, arecompared with the tabulated wavelengths of the diffuse interstellar bands. In the case of the A²Π_u–X²Π_g transition of C₇^- the origin and three intense bands in the gas-phase spectrum match, within ±0.2 nm error limits, diffuse interstellar bands which have comparable FWHMs and equivalent widths.