US EPA

5707254 

Journal Article 

Structures and cis-to-trans photoisomerization of hexafluoro-1,3-butadiene radical cation: electron spin resonance and computational studies 

Xiao, HY; Cao, J; Liu, YJ; Fang, WH; Tachikawa, H; Shiotani, M 

2007 

1 

DUPE - Journal of Physical Chemistry A
ISSN: 1089-5639
EISSN: 1520-5215 

111 

24 

5192-5200 

English 

17523606 

10.1021/jp070672c 

WOS:000247216600010 

The s-cis and s-trans isomer radical cations of hexafluoro-1,3-butadiene (s-cis-HFBD+ and s-trans-HFBD+) were generated by a gamma-irradiated solid solution of the neutral HFBD molecule in solid matrix at 77 K and observed by means of electron spin resonance (ESR) and electronic spectroscopies. In comparing the experimental isotropic and anisotropic 19F hyperfine splittings with the computational ones by the DFT B3LYP and MP2 methods, the generated s-cis-HFBD+ and s-trans-HFBD+ radical cations were confirmed to be 2A2 and 2Bg electronic ground states in C2v and C2h symmetries, respectively. The present spectroscopic study revealed that the relative abundance of s-cis-HFBD+ to s-trans-HFBD+ was 4.0 immediately after being formed by gamma-irradiation, and subsequently most s-cis-HFBD+ was isomerized to s-trans-HFBD+ by visible-light illumination with 500-600 nm wavelength. The process of nonplanar HFBD ionizing to form stable planar s-cis- and s-trans-HFBD+ and the reaction mechanism of the cis-to-trans photoisomerization were discussed by (MS-)CASPT2//CASSCF calculated vertical excitation energies (Tv) and torsional potential energy curves (TPECs) of HFBD and HFBD+.