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C[sub 3]H[sup 2+, sub 5], formed by electron impact ionization of propane, undergoes metastable decay into C[sub 2]H[sub 2, sup +] + CH[sub 3, sup +]. We have monitored this reaction in a magnetic mass spectrometer of reversed geometry that is equipped with two electric sectors (BEE geometry). Three different techniques were applied to identify the fragment ions and determine the kinetic-energy release (KER) of spontaneous Coulomb explosion of C[sub 3]H[sup 2+, sub 5] in the second and third field free regions of the mass spectrometer. The KER distribution is very narrow, with a width of about 3% [root-mean square standard deviation]. An average KER of 4.58 ± 0.15 eV is derived from the distribution. High level ab initio quantum-chemical calculations of the structure and energetics of C[sub 3]H[sup 2+, sub 5] are reported. The activation barrier of the reverse reaction, CH[sub 3, sup +] + C[sub 2]H[sub 2, sup +] (vinylidene), is computed. The value closely agrees with the experimental average KER, thus indicating that essentially all energy available in the reaction is partitioned into kinetic energy. [ABSTRACT FROM AUTHOR]

Abstract: We have measured the kinetic energy release distributions for unimolecular C2 loss from singly and multiply charged endohedral La@C80 z+ and La@C80 z+ ions for charge states z =1–3. Using finite heat bath theory, we deduce the dissociation energies for loss of C2. The charge state z has no statistically significant effect on the dissociation energies. The dissociation energies of endohedral fullerene ions are larger than those of the corresponding empty fullerene ions by a few tenths of an electron volt, but the differences are barely statistically significant. The small differences also imply that the complexation energies of La@C n z+ and La@C n −2 z+ are identical within the experimental errors, for n =80 and 82 and all charge states. [Copyright &y& Elsevier]

The recent addition of (i) a third sector field to our two sector field mass spectrometer (resulting in a BE1E2 field configuration) and of (ii) a high performance electron gun enables us now to study in detail the time dependence of the kinetic energy release distribution (KERD) over a relatively wide range of cluster ion lifetimes. Using this newly constructed device we have studied here for the first time KERDs and deduced binding energies BEs (using finite heat bath theory) of large rare gas cluster ions (an upper size limit in earlier studies arose from the fact that different naturally occurring isotopes will contribute to a chosen metastable peak when the size exceeds a certain value) and in addition of fullerene ions smaller and larger than C60+ (here again contaminating coincidences did not allow such studies earlier). Moreover, high precision KERD measurements for the decay of rare gas dimer ions in conjunction with model calculations (using recently calculated potential energy curves for the rare gas dimer ions) also enable us to obtain information on the dynamics and the mechanisms of the underlying spontaneous decay reactions Rg2+∗ → Rg+ + Rg. In addition, we are also reporting here a novel method (unified breakdown graph method) to determine cluster ion binding energies using a recently constructed tandem mass spectrometer BESTOF allowing us to measure fragmentation patterns arising from the unimolecular decay of molecular cluster ions induced by surface collisions. The fragmentation and reaction patterns of protonated ethanol cluster ions investigated here clearly demonstrate in contrast to some of the earlier cluster ion studies that unimolecular dissociation kinetics determines the formation of product ions in the surface-induced decomposition. [ABSTRACT FROM AUTHOR]