Vacuum ultraviolet-infrared photo-induced Rydberg ionization spectroscopy: C–H stretching frequencies for trans-2-butene and trichloroethene cations.

We have demonstrated the two-color vacuum ultraviolet (VUV)-infrared (IR) photoinduced Rydberg ionization (PIRI) experiment. Trichloroethene (ClCH==CCl[sub 2]) and trans-2-butene (trans-CH[sub 3]CH==CHCH[sub 3]) were prepared in Rydberg states in the range of effective principal quantum number n[sup *]≈7–93 by VUV excitation prior to IR-induced autoionization. The observed VUV-IR-PIRI spectra are found to be independent of n[sup *], suggesting that the electron Rydberg orbital is conserved, i.e., the Rydberg electron is behaving as a spectator during the excitation process. The observed IR active C–H stretching vibrational frequencies ν[sub 12][sup +]=3072±5 cm[sup -1] for ClCH==CCl[sub 2][sup +] and ν[sub 23][sup +]=2908±3 cm[sup -1], ν[sub 25][sup +]=2990±10 cm[sup -1] and ν[sub 30][sup +]=3022±10 cm[sup -1] for trans-CH[sub 3]CH==CHCH[sub 3][sup +] are compared with predictions based on ab initio quantum-chemical procedures and density functional calculations. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]