Spectroscopic characterization of a series of polyyne–iodine molecular complexes H(CC)nH(I6) of n = 5–9

A series of molecular complexes, C2nH2I6 (n = 5–9), formed from size-selected hydrogen-end-capped polyyne, H(CC)nH, and iodine molecules was characterized by UV–vis and IR absorption spectroscopy for elucidating location and geometry of iodine atoms in the complex. The IR lines for the CH-stretching σu fundamental at 3305 cm−1 and CH-bending πu fundamental at 625 cm−1 for C2nH2 (n = 5–7) in CCl4 were red-shifted by 220 and 15 cm−1, respectively, for its complex of C2nH2I6. A few lines were intensified in the low-frequency region of 850–1450 cm−1 for CC-stretching σu modes of polyynes in the complex.