FAR INFRARED BENDING MODE FOR $C_{4}$ TRAPPED IN $Ar^{1}$

Author Institution: Department of Physics, Texas Christian University; Chemical Engineering, Yale University; Department of Physics, Texas Christian UniversityThe bending mode of the $C_{4}$ chain has been observed for the first time at $172.4 cm^{-1}$ 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 $^{13}C$ isotopic data; is consistent with the earlier $identification^{2}$ of the antisymmetric $C=C$ stretching mode at $1543.4 cm^{-1}$ (found more recently in the gas $phase^{3}$ at $1548.937 cm^{-1}$; and is in agreement with the predictions of ab initio $calculations.^{4}$ $^{1}$Supported by the W.M. Keck Foundation and the Welch Foundation (Grant P-0786). $^{2}$L.N. Shen and W.R.M. Graham, J. Chem. Phys. 91, 5115 (1989). $^{3}$J.R. Heath and R.J. Sakally, J. Chem. Phys. 94, 3271 (1991). $^{4}$D. Michalska, H. Chojnacki, B. A. Hess, and L.J. Schaad, Chem. Phys. Lett. 141, 376 (1987)