Knowledge Bank

The bending mode of the $C4$ chain has been observed for the first time at $172.4cm-1$ in the Fourier transform spectrum of the vacuum ultraviolet photolysis products of 1,3-butadiene and acetylene trapped in Ar at 10 K. The assignment is confirmed by $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ isotopic data; is consistent with the earlier $identification2$ of the antisymmetric $C=C$ stretching mode at $1543.4cm-1$ (found more recently in the gas $phase3$ at $1548.937cm-1$; and is in agreement with the predictions of ab initio $calculations.4$ $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$Supported by the W.M. Keck Foundation and the Welch Foundation (Grant P-0786). $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$L.N. Shen and W.R.M. Graham, J. Chem. Phys. 91, 5115 (1989). $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$J.R. Heath and R.J. Sakally, J. Chem. Phys. 94, 3271 (1991). $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$D. Michalska, H. Chojnacki, B. A. Hess, and L.J. Schaad, Chem. Phys. Lett. 141, 376 (1987).