Vacuum ultraviolet laser pulsed field ionization-photoelectron study of cis-dichloroethene

The vacuum ultraviolet (VUV) laser pulsed field ionization photoelectron (PFI-PE) spectrum of cis-dichloroethene (cis-ClCH=CHCl) has been measured in the energy region of 77 600-79 500 cm^-1. On the basis of the semiempirical simulation of the origin PFI-PE band, we have obtained the IE (cis-ClCH=CHCl) to be 77 899.5 ± 2.0 cm^-1 (9.658 39 ± 0.000 25 eV). The assignment of the vibrational bands resolved in the VUV-PFI-PE spectrum are guided by high-level ab initio calculations of the vibrational frequencies for cis-ClCH=CHCl⁺ and the Franck-Condon factors for the ionization transitions. Combining the results of the present VUV-PFI-PE measurement and the recent VUV-infrared-photoinduced Rydberg ionization study [P. Wang et al., J. Chem. Phys. 124, 064310 (2006)], the vibrational frequencies for eleven of the twelve vibrational modes of cis-ClCH=CHCl⁺ have been experimentally determined: v₁⁺(a₁) =181 cm^-1, v₂⁺(a₂) =277 cm^-1, v₃⁺(b₂) =580 cm^-1,v₄⁺(b₁) =730 cm^-1, v₅⁺(a₁) =810 cm^-1, v₆⁺(a₂) =901 cm^-1, v₈⁺(a₁) =1196 cm^-1, v₉⁺(b₂) =1348 cm^-1, v₁₀⁺(a₁) =1429 cm^-1, v₁₁⁺(b₂) =3067 cm^-1, and v₁₂⁺(a₁) =3090 cm^-1). These values are compared to theoretical an harmonic vibrational frequencies obtained at the MP2/6-311G(2df,p) and CCSD(T)/6-311G(2df,p) levels. The IE prediction for cis-ClCH=CHCl has also been calculated with the wave function based CCSD(T)/CBS method, which involves the approximation to the complete basis set (CBS) and the high-level correlation corrections. The theoretical IE (cis-ClCH=CHCl) =9.668 eV thus obtained is found to have a deviation of less than 10 meV with respect to the experimental IE value. © 2006 American Institute of Physics.