High resolution photoabsorption spectrum of hexafluoro-1,3-butadiene (1,3-C 4F 6) as studied by vacuum ultraviolet (VUV) synchrotron radiation

In this Letter we present a high resolution VUV photoabsorption spectrum of hexafluoro-1,3-butadiene (1,3-C 4F 6), over the wavelength range 113-247 nm (11.0-5.0 eV). The spectrum reveals several new features not previously reported in the literature. The assignment of the observed valence and Rydberg transitions and the associated vibronic series is presented based on our recent ab initio calculations on the vertical excitation energies of C 4F 6 isomers. The dominant excitation has been assigned to the υ 1′(a) CC stretching mode in the (5 1A ← 1 1A, 3p a ← π a(20a)) and (7 1A ← 1 1A, 3p b ← π b(19b) ) transitions, with mean energies of 0.201 and 0.188 eV, respectively. The measured absolute photoabsorption cross section has been used to calculate the photolysis lifetime of 1,3-C 4F 6 in the upper stratosphere (20-50 km).