Observational Studies Relating To Diffuse Interstellar Bands

We observed a series of five or six DIBs lines with a nearly constant spacing of about 35 cm−1 around 6800 A by using a spectrometer with a wavelength resolution of λ/Δλ=75,000. We obtained similar intensities in HD 21389, HD 41117, HD 43384, HD 198478, and HD 206165. As a candidate of these DIBs carrier, a perpendicular vibronic band of CH2X type molecules has been proposed by Glinski and Nuth (PASP, 107, 453, 1995), where X is a heavy atom or linear carbon chain. Although the 35 cm−1 intervals are interpreted by assuming only ortho lines are detected, we could find none of the spectral lines originating from para levels. We simulated the spectra of quasi‐linear molecules such as HNCX, and found that a high temperature is required for explanation of the observed spectra. Thus we concluded that the carrier of series of DIBs appeared near 6800 A is not explained by the perpendicular vibronic band of CH2X and quasi linear HNCX type molecules. Other candidates are discussed.