Aminoacetylene and Its Mono‐ and Dication—Identification of Potentially Interstellar Molecules

Abstract

oxidation. Since four electrons are required for the formation of an 02-molecule, a water-oxidation can only be achieved if the 1 e-processes can be efficiently coupled. This is obviously not the case in homogeneous phases, but is so in heterogeneous phases.The heterogeneous water-oxidation system described here is of special interest with regard to the evolution of oxygen in photosynthesis. It has already been suggested['.'-'] that the microheterogeneous environment around the manganese centers and the close proximity of the manganese atoms to one another are responsible for water-splitting in photosynthesis. This is supported by our finding that the complexes 1 and 2 are only catalytically active in the solid form. It is conceivable that four molecules of the binuclear manganese complex may be oxidized by four adjacent Ce'" ions to produce a four-electron depletion center on the surface. This oxidizing center would then lead to the four-electron oxidation of two molecules of weakly bound water with subsequent evolution of oxygen.

What Ion Is Generated When Ionizing Acetonitrile?

“…Therefore, the CID mass spectra mentioned earlier are necessarily characterizing mixtures of structures 1 and 2 , with slightly more 1 being present when acetonitrile is ionized as compared to when butyronitrile or chloroacetonitrile are dissociatively ionized. This conclusion was also drawn by Choe 5 and is consistent with a recent surface-induced reaction study by Mair et al It also accounts for some of the observed variation in the CID mass spectra between instruments (in which source conditions and experimental time scales will all be slightly different). −

1 Potential energy diagram for the interconversion of CH 3 CN +• and CH 2 CNH +• (calculated at the G3 level of theory) and their lowest energy dissociation products (see text).

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“…These assignments are based on the relative peak heights in CID mass spectra. The key distinguishing factor that has been used in the literature is the CH 2 + /CH 3 + ( m / z 14:15) ratio. − In all cases, structure 1 (assumed to be generated by ionizing acetonitrile) was characterized by a peak at m / z 15 that has roughly twice the relative abundance as that for 2 (generated by dissociative ionization of butyronitrile). − This holds true for our CID experiments done on the Rome VG Micromass ZABSpec oa-TOF under conditions of high mass resolution . In the present experiments, the CID of ionized acetonitrile yielded a mass spectrum with a ratio of m / z 14:15 of 10, whereas the C 2 H 3 N +• ion generated from dissociative ionization of butyronitrile gave a ratio of 24.…”

“…It has long been assumed that ionizing neutral acetonitrile produces ions with the same atomic connectivity, CH 3 CN +• ( 1 ). − Other C 2 H 3 N +• include CH 3 NC +• (assumed to be formed by ionizing isocyanomethane), whereas dissociative ionization of larger nitriles has been shown to yield a different structure that has been assigned to ionized ketenimine CH 2 CNH +• ( 2 ). − Dissociative ionization of imidazole and pyrazole was postulated to produce the linear CHCHNH +• structure . These assignments are based on the relative peak heights in CID mass spectra.…”

“…A ratio of 22 was obtained for the C 2 H 3 N +• ion formed upon dissociation of protonated chloroacetonitrile. The absolute value of the m / z 14:15 ratio varies with instrument, − the reason for which will become apparent below.…”

Selective Generation of the Radical Cation Isomers [CH3CN]•+ and [CH2CNH]•+ via VUV Photoionization of Different Neutral Precursors and Their Reactivity with C2H4

“…Hence, when working with standard ionization sources using 70 eV energy electrons, it is difficult to estimate the fraction of the various isomers produced. The experimental characterization of the isomers generated upon ionization of CH 3 CN has created significant disputes over the years and various experimental techniques have been used for this purpose, ranging from the study of the ratio of the CH 3 + /CH 2 + fragments by collision-induced dissociation experiments − to selected ion–molecule reactions. , Theoretical calculations have shown that the isomerization from [CH 3 CN] •+ into [CH 2 CNH] •+ is exothermic by about 2 eV (more specifically 2.13 eV according to Mair et al, 2.15 according to Choe et al, and 2.40 eV for DePetris et al), but it is hampered by a barrier smaller than 0.95 eV (0.85 eV according to Choe et al and 0.73 eV according to DePetris et al). Despite the small differences in the predicted energetics, the important message is that upon removal of one electron from acetonitrile a substantial rearrangement in the structure occurs and the [CH 3 CN] •+ is not the most stable of all the possible [C 2 H 3 N] •+ isomers.…”