Vacuum Ultraviolet (VUV) Pulsed Field Ionization−Photoelectron and VUV−IR Photoinduced Rydberg Ionization Study of trans-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 v 1 + = 163 cm - 1 , v 3 + = 367 cm - 1 , v 4 + = 871 cm - 1 , v 5 + = 915 cm - 1 , v 6 + = 944 cm - 1 , v 8 + = 1235 cm - 1 , v 9 + = 1258 cm - 1 , v 1 0 + = 1452 cm - 1 . The distinct feature of the VUV-PFI-PE spectrum is the strong vibrational progression of the v 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 v 1 1 + (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.