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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]

We have measured the kinetic energy release (KER) distributions for electron-induced dissociation of mass-selected molecular parent and fragment ions of propane. They are compared with distributions determined for spontaneous (metastable) dissociation. The average KER for induced dissociation of C[sub 3]H[sub 8][sup +] into C[sub 3]H[sub 7][sup +] is 13.2±1.2 meV, about 42% larger than for the spontaneous reaction. This large difference is attributed to the dramatically reduced time at which the induced reaction can be sampled. In contrast, the KER for dissociation of C[sub 3]H[sub 7][sup +] into C[sub 3]H[sub 5][sup +], which is characterized by a large reverse activation energy, is hardly affected by the experimental time scale. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The dissociation energies of singly and multiply charged Sc3@C78 and Sc3N@C80 towards loss of C2 are detailed using finite heat bath theory. The complexation energies are for a given charge state and within the experimental uncertainty, and are identical for n=76, 78, and 80

Reports on the achievement of direct mass spectrometric evidence that fullerene ions undergo unimolecular dissociation by sequential emission of two C2 units. Comparison of experimental and theoretical breakdown graphs; Reaction channels accessible to excited fullerenes; Importance of thermal radiation for neutral and charged C[sub 60].

The two-photon resonant absorption of Kr2(1Σ+g) has been measured via (2+1) multiphoton ionization studies in the energy range 91 750–92 420 cm-1. Two vibrational progressions are observed. One of them is attributed to the atomic 4p5(2P3/2)5p[5/2]2 state, implying D’0 =220 cm-1. A long progression is assigned as correlating with the 4p5(2P3/2)5p[3/2]2 state, implying D0 ≥1480 cm-1. [ABSTRACT FROM AUTHOR]

Ammonia clusters, produced via supersonic expansion, are subjected to multiphoton ionization using a tunable pulsed laser. The products of ionization and subsequent dissociation processes are investigated using a time-of-flight mass spectrometer equipped with a reflectron (reflecting electric field). Cluster ions containing more than 65 ammonia molecules were formed via internal ion molecule reactions taking place within the initially ionized aggregate. The proton transfer reaction which ensues leads to substantial excess internal energy and subsequent cluster decomposition. Dissociation due to both collisional and unimolecular processes was identified in the field-free region. Studies of the dynamics of dissociation were made for species up to the protonated 16-mer; the loss of up to at least five monomer units following cluster ion formation was observed. Results of an investigation of the influence of laser fluence and the energy of the ionizing photons are also presented. [ABSTRACT FROM AUTHOR]

Clusters of argon, krypton, and xenon are grown in a free jet and ionized by electron impact. The size of these clusters, (Rg)+n, extends up to n[bar_over_tilde:_approx._equal_to]1000. Individual cluster sizes are mass resolved up to n[bar_over_tilde:_approx._equal_to]570 in the case of Ar+n. The well known, but puzzling differences in the size distributions of Kr and Xe clusters disappear beyond n[bar_over_tilde:_approx._equal_to]130, while those between Ar and Xe disappear beyond n[bar_over_tilde:_approx._equal_to]220. The most pronounced ‘‘magic numbers’’ in the distributions of large cluster ions occur at n=147 (148 for Ar), 309, and 561, in striking agreement with the number of atoms required to build icosahedral clusters with 3, 4, and 5 complete coordination shells, respectively. Closure of the 6th icosahedral coordination shell is indicated by another strong intensity drop at n[bar_over_tilde:_approx._equal_to]923 in the unresolved part of the spectra. Several additional intensity extrema are observed between major shell closures. A simple structural model, assuming an icosahedral core decorated by the additional atoms, accounts for these anomalies reasonably well up to n=561. [ABSTRACT FROM AUTHOR]

It has recently been suggested that the lifetime of the lowest triplet state in multiphoton-excited C[sub 60] is much longer than anticipated. If true, this would invalidate the assumption of internal thermal equilibrium in the description of statistical decay processes of the molecule, such as thermionic emission. We present pump–probe measurements which show that the lifetime is below 1 μs at vibrational excitation energies of 6.5 eV, and that it decreases further to 40 ns at 10 eV. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]