An ab initio study on noble gas inserted halogenated acetylene: HNgCCX (Ng = Kr and Xe; X = halogen).

Although HNgCCX (Ng = Kr and Xe; X = F and Cl) have been identified in cryogenic matrices, similar Br and I analogues have not been prepared so far. In this paper, the nature of HNgCCX (Ng = Kr and Xe; X = F, Cl, Br and I) have been investigated by ab initio methods. The main characteristic absorption peak of HNgCCX is the v H-Ng, which decreases as X varies from F to I. Moreover, the H-Xe bond is stronger than the H-Kr bond. The v C≡C and v C-X exhibit red- and blue-shift characters, respectively, especially the C-X bond is abnormal blue-shift halogen bond. AIM results show that the H-Ng bond is essentially covalent bond and the covalent character of H-Xe bond is underestimated, and the trend of the covalent character is C-Cl > C-Br > C-F > C-I. Although HNgCCX is instable thermodynamically with respect to Ng + HCCX, it is kinetically stable with respect to the two-/three-body channels due to the relatively larger energy barriers. The three-body channels of HNgCCX is the main decomposition channel, and the kinetically stability of HXeCCX is more than its Kr analogues. This study is helpful for the preparation of new HNgCCX in cryogenic matrices.