Vacuum Ultraviolet (VUV) Pulsed Field Ionization−Photoelectron and VUV−IR Photoinduced Rydberg Ionization Study of <i>trans-</i>Dichloroethene

Abstract

The vacuum ultraviolet (VUV) pulsed field ionization−photoelectron (PFI−PE) spectrum for trans -dichloroethene ( trans -ClCH CHCl) has been measured in the energy range 77 600−79 200 cm -1 . On the basis of the spectral simulation of the origin VUV−PFI−PE vibrational band, we have determined the IE( trans -ClCH CHCl) to be 77 678.4 ± 2.0 cm -1 (9.630 97 ± 0.000 25 eV). The vibrational bands resolved in the VUV−PFI−PE spectrum of trans -ClCH CHCl are assigned on the basis of ab initio vibrational frequencies and calculated Franck−Condon factors for the ionization transitions, yielding eight vibrational frequencies ν 1 + = 163 cm -1, ν 3 + = 367 cm -1, ν 4 + = 871 cm -1, ν 5 + = 915 cm -1, ν 6 + = 944 cm -1, ν 8 + = 1235 cm -1, ν 9 + = 1258 cm -1, ν 10 + = 1452 cm -1 . The distinct feature of the VUV−PFI−PE spectrum is the strong vibrational progression of the ν 3 + (C Cl stretching) mode of trans -ClCH CHCl +, which is consistent with the theoretical geometry calculation, predicting a significant change in the C Cl bond distance upon photoionization of trans -ClCH CHCl. We have also determined the frequency (3068 cm -1 ) for the ν 11 + (C H stretching) vibrational mode of trans -ClCH CHCl + by employing the VUV−IR-photoinduced Rydberg ionization (VUV−IR−PIRI) method. The VUV−IR−PIRI spectra for trans -ClCH CHCl prepared in the effective principal quantum numbers, n * = 14 and 36, are found to be identical, supporting the previous conclusion that the Rydberg electron behaves as a spectator; i.e., the Rydberg electron orbital is conserved during the IR excitation of the ion core.