Highhyphen;pressure Raman study of a onehyphen;dimensional hydrogenhyphen;bonded crystal of cyanoacetylene

摘要

At room temperature, cyanoacetylene undergoes a liquidndash;solid transition at 70plusmn;30 MPa and further a polymerization reaction at 1.5 GPa. Raman spectra indicates that the crystal structure of the highhyphen;pressure phase is isomorphic with the monoclinic lowhyphen;temperature structure (P21/m,Z=2), in which linear cyanoacetylene molecules are joined with CH NC hydrogen bonds to form infinite onehyphen;dimensional chains. The internal stretching frequency of the Cndash;H proton donor decreases wtih increasing pressure, while that of the C 3/4 N proton acceptor increases. The librational modes associated with the rotational motions of the rigid molecules show large shifts to higher frequencies with pressure. The observed frequency shifts are attributed to the strengthening of the CHsdot;sdot;sdot;NC hydrogen bond in the onehyphen;dimensional molecular chain.