[P-CG20] Origin and evolution of materials in space

[PCG20-P05] Laboratory spectroscopy of ICN⁺ to estimate profiles of interstellar absorption lines by halogen cyanide cations

*Mitsunori Araki¹, Takumi Ito¹, Shoma Hoshino¹, Koichi Tsukiyama¹ (1.Department of Chemistry, Faculty of Science Division I, Tokyo University of Science)

Keywords:ICN+, interstellar absorption line, Laboratory spectroscopy

Diffuse interstellar bands (DIBs) are optical absorption lines by electronic transitions of interstellar molecules in diffuse clouds. Six hundred DIBs have been reported so far. Although the five of them were identified as the fullerene cation C₆₀⁺, almost all bands are not identified yet. As a hint of DIB carriers, the presence of this ion infers that molecules in a diffuse cloud are easily ionized. Additionally, the molecules would frequently contain a cyano group and occasionally include a halogen atom, because both elements exist in space. Hence, halogen cyanide cations are good carrier candidates. To identify origin molecules of DIBs, laboratory data of band profiles of electronic transitions are essential as well as those of their wavelengths. Generally, a band profile is determined by a structural change of an electronic transition. However, the direct observations of the structural changes for the Sigma–Pi electronic transitions of the halogen cyanide cation have not been reported thus far. In this work, the electronic transition of ICN⁺, which is one of the halogen cyanide cations, was observed for the first time by cavity ringdown spectroscopy. Analysis of the observed spectrum suggests that the profiles of the abortion bands of the halogen cyanide cations have symmetric structures irrespective of diffuse-cloud temperature. This information allows us to search the halogen cyanide cations in space.