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Vibrationally resolved photoelectron anisotropy parameters and branching ratios for the N2+X²Σg+ state have been measured between the ionization threshold and ~16.7 eV to study the influence of autoionization on the photoionization dynamics. In this energy range the ion yield curve exhibits extensive structure due to autoionizing Rydberg or valence states. Some of these Rydberg states belong to series converging onto the A ²Πu limit but, close to the ionization threshold, states belonging to series converging onto vibrationally excited levels of the X²Σg+ state are also observed. At photon energies free from the influence of neutral excited states, the measured vibrational branching ratios correlate with the Franck-Condon factors for direct ionization. However, strong deviations are observed when the excitation energy corresponds with a transition into an autoionizing state. An attempt to interpret these variations using Franck-Condon factors connecting the neutral excited state and the final ionic state proved unsuccessful. This failure suggests that the intermediate states might not be pure Rydberg states. Electronic and, close to threshold, vibrational autoionization affects the vibrationally resolved photoelectron anisotropy parameters, leading to a significant reduction in the fairly high β-values determined for non-resonant ionization. Photoelectron images of the N2+X²Σg+ state recorded close to the v+ = 1 or the v+ = 2 ionization thresholds suggest that electronic autoionization results in rotational branch populations that differ from those due to direct, non-resonant, photoionization. [ABSTRACT FROM AUTHOR]

Using vacuum-ultraviolet (VUV) synchrotron radiation, threshold and dissociative photoionization of cyanopropyne (CH 3 C 3 N) in the gas phase have been studied from 86 000 cm −1 up to 180 000 cm −1 by recording Threshold-PhotoElectron Spectrum (TPES) and PhotoIon Yield (PIY). Ionization energies of the four lowest electronic states X ̃ + 2 E , A ̃ + 2 A 1 , B ̃ + 2 E and C ̃ + of CH 3 C 3 N + are derived from the TPES with a better accuracy than previously reported. The adiabatic ionization potential of CH 3 C 3 N is measured as 86 872 ± 20 cm −1 . A description of the vibrational structure of these states is proposed leading to the first determination of the vibrational frequencies for most modes. The vibrational assignments of the X ̃ + state are supported by density functional theory calculations. In addition, dissociative photoionization spectra have been recorded for several cationic fragments in the range 12–15.5 eV (96 790–125 000 cm −1 ) and they bring new information on the photophysics of CH 3 C 3 N + . Threshold energies for the cationic dissociative channels leading to CH 2 C 3 N + , CHC 3 N + , HC 3 H + , HCNH + and CH 3 + have been measured for the first time and are compared with quantum chemical calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cationic isomers of methanimine generated via dissociative photoionization. • Reactive cross sections and branching ratios with C 2 H 4 as a function of collision energy and photon energy. • Different cation isomers react differently and calculations helps understanding. • Main products are due to H loss from stable adducts: reactions lead to growth of complex ions. • Barrierless reactions → feasible for the synthesis of large N-containing molecules in low T environments. Experimental and theoretical studies are presented on the reactivity of H 2 CNH•+ (methanimine) and HCNH 2 •+ (aminomethylene) with ethene (C 2 H 4). Selective isomer generation is performed via dissociative photoionization of suitable neutral precursors and reactive cross sections and branching ratios are measured as a function of photon and collision energies. Differences between isomers' reactivity are discussed in light of ab-initio calculations on reaction mechanisms. The main products, for both isomers, are H-elimination, most likely occurring from covalently bound adducts (giving c-CH 2 CH 2 CHNH+/CH 2 NHCHCH 2 +) and H• atom transfer to yield H 2 CNH 2 +. The astrochemical implications of the results are briefly addressed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cationic isomers of methanimine generated via dissociative photoionization. • Isomers react with methane by H atom transfer to give protonated methanimine. • Reactive cross sections are given as a function of collision energy and photon energy. • Different cation isomers react differently and calculations help understanding. • Reactions are relevant for Titan's atmosphere. Experimental and theoretical studies are presented on the reactions of the isomeric radical cations H 2 CNH + and HCNH 2 + with CH 4. Ionic isomers were generated selectively by VUV dissociative photoionization of azetidine and cyclopropylamine precursors respectively. Both exclusively give H 2 CNH 2 + plus CH 3 as products, but differences are observed related to a competition between stripping and complex-mediated H-transfer. Astrochemical implications for Titan's atmosphere are briefly discussed, where the presence of methanimine (H 2 CNH), a key prebiotic molecule and a potential precursor for tholins, is proposed on the basis of atmospheric models and the observation of CH 2 NH 2 + ions in Cassini mass spectrometric data. [ABSTRACT FROM AUTHOR]