Appearance potentials and heats of formation of a number of C2H5O+ and C2H6N4" ions have been determined. The 20 processes examined were chosen such that, based on the structure of the parent molecule, 4 isomers of C2HsO+ and 5 isomers of C2HeN+ would be formed. Thermochemical evidence was found which indicated that those processes expected to yield CH2CH2OH+ and CH2CH2NH2+ involved rearrangements forming protonated ethylene oxide and protonated ethylenimine. The following heats of formation were obtained: CH3CH-OH+, 140 ± 1 kcal/mol; CH30=CH2+, 163 ± 1 kcal/mol; c-C2H4OH+, 165 ± 2 kcal/mol; CH3CH20+, 198 ± 2 kcal/mol; CH3CH=NH2+, 154 ± 4 kcal/mol; CH3NH==CH2+, 154 ± 4 kcal/mol; c-C2H4NH2+, 173 db 2 kcal/mol; CH3NCH3+, 206 ± 4 kcal/mol. Data for CH3CH2NH+ indicate a heat of formation on the order of 200 ± 10 kcal/mol but this is uncertain because of the possibility of rearrangement to CH3CH=NH2+. Comments are made on the use of a doublefocussing mass spectrometers electrostatic sector as a probe for excess ion kinetic energies and evidence found for the occurrence of a significant amount of excess energy in the formation of CH3NCH3+ from N, IV-dimethyl-terí-buty lamine.
The translational energy released in the unimolecular loss of H* from metastable methane ions has been examined and found to have a significant temperature dependence. Reaction mechanisms of the barrier traversal, tunnelling, and electronic predissociation types are all inconsistent with the observed temperature effect if centrifugal effects are neglected. The observed temperature dependence of the kinetic energy release correlates well with the variation in centrifugal barrier height with rotational energy derived from a simple form of Langevin collision theory. It is also in agreement with the more rigorous treatment of Klots which allows tunnelling through the centrifugal barrier.
The ion-molecule reactions in propane and in methane–propane mixtures have been studied using an ion-trapping technique and rate coefficients have been measured for the reactions occurring. In pure propane the C2H5+ primary ions react by H− transfer to form C3H7+ whereas C2H4+ reacts to form C3H6+ (25%) and C3H7+ (75%). Using isotopically labelled propanes it was found that both n-propyl and i-propyl ions were formed with the n-propyl ions reacting slowly to produce i-propyl ions. In various deuterium labelled methane–propane mixtures C(H,D)5+ reacts with the propane with a rate constant of ∼1.5 × 10−9 cm3 molecule−1 s−1 in agreement with the calculated collision rate. It is shown that no hydrogens from the CH5+ ion are incorporated in the product ions which are found to be C2H5+ (70%), (CH3)2CH+ (25%), and CH3CH2CH2+ (5%).
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