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Through a combined experimental and theoretical approach, we study thenonadiabatic dynamics of the prototypical ethylene (C$_2$H$_4$) molecule upon$\pi \rightarrow \pi^*$ excitation with 161 nm light. Using a novelexperimental apparatus, we combine femtosecond pulses of vacuum ultraviolet(VUV) and extreme ultraviolet (XUV) radiation with variable delay to performtime resolved photo-ion fragment spectroscopy. In this second part of a twopart series, the extreme ultraviolet (17 eV$ < h \nu < 23$ eV) probe pulses aresufficiently energetic to break the C-C bond in photoionization, or photoionizethe dissociation products of the vibrationally hot ground state. Theexperimental data is directly compared to ab initio molecular dynamicssimulations accounting for both the pump and probe steps. Enhancements of theCH$_2^+$ and CH$_3^+$ photoion fragment yields, corresponding to moleculesphotoionized in ethylene (CH$_2$CH$_2$) and ethylidene (CH$_3$CH) likegeometries are observed within 100 fs after $\pi \rightarrow \pi^*$ excitation.Quantitative agreement between theory and experiment on the relative CH$_2^+$and CH$_3^+$ yields provides experimental confirmation of the theoreticalprediction of two distinct transition states and their branching ratio (Tao, etal. J. Phys. Chem. A. 113, 13656 (2009)). Fast, non-statistical, elimination ofH$_2$ molecules and H atoms is observed in the time resolved H$_2^+$ and H$^+$signals.

Ultrafast Internal Conversion in Ethylene. II. Mechanisms and Pathways for Quenching and Hydrogen Elimination