Laboratory high resolution spectroscopy for Interstellar matter in the optical region

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The diffuse interstellar bands (DIBs) were first discovered in the optical absorption spectra on stars in 1922. Although several hundreds DIBs were detected already, DIBs still remain the longest standing unsolved problem in spectroscopy. It has not been known that what kind molecules have these absorptions. One of the best approaches to identify DIBs can be the following procedure: 1) a generation of a DIBs candidate molecule in laboratory, 2) measurements of frequencies of electronic transitions of the molecule, and 3) comparisons between the frequencies and astronomically observed spectra.To be able to solve the DIBs problem, we have been developed a discharge-emission spectrometer system. A hollow cathode was used to generate molecular ions in a discharge, since it has been suggested that molecular ions can be probable candidates of DIBs origins. The discharge was produced by a pulsed voltage of 1500V. A wide wavelength range of our system was covered by two spectrometers HORIBA Jobin Yvon iHR320 (the 200-800 nm wavelength range using three gratings having groove densities 1200 and 1800 gr/mm) and Actron Research Corporation Spectro pro275 (the visible - 1600 nm wavelength range, 600 gr/mm). The dispersed discharge-emission was detected by a photomultiplier and recorded via the lock-in amplifier (Femto LIA-MV-200-L).In observing a discharge of Argon gas, optical transitions of Argon ion were strongly detected having comparable intensities with those of Argon neutral. The ion can be effectively produced by the hollow-cathode effect in the discharge.