Observations of diffuse interstellar Bands(1) attributed to C–7.
McCALL B.J., YORK D.G. and OKA T.
Abstract (from CDS):
Recent advances in laboratory gas-phase spectroscopy of large molecules and their ions permit a direct comparison between the diffuse interstellar bands (DIBs) and proposed carriers. On the basis of gas-phase data, Tulej et al. recently suggested that five A2Πu⟵X2Πg electronic transitions of the linear carbon-chain anion C–7 match with DIBs. We have obtained high-resolution visible spectra of four reddened stars (HD 46711, HD 50064, HD 183143, and Cyg OB2 12) to make a detailed comparison with the C–7 laboratory data. Our data show that three of the C–7 bands (000 at 6270.2 Å, 310 at 6064.0 Å, and 120310 at 4963.0 Å) are in good agreement with DIBs in wavelength and relative intensity. A fourth band (110 at 5612.8 Å) also agrees in intensity but is apparently off by 2 Å in wavelength. All other laboratory bands of C–7 are not expected to be detectable in astronomical spectra with the current level of sensitivity. The gas-phase spectrum of C–7 agrees with the DIBs better than that of any previously proposed molecule. However, the question of whether C–7 is a DIB carrier cannot be definitively answered until (1) better laboratory measurements confirm, refute, or explain the wavelength discrepancy for the 110 band and/or (2) better astronomical spectra reveal the presence or absence of other C–7 bands.