Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.     

Sounding rocket measurements of suprathermal ion acceleration

Transverse ion acceleration has been observed at rocket altitudes between 500 and 1000 km due to the injection of 100-200-eV argon plasma, auroral electron precipitation, and the injection of electromagnetic waves. Field-aligned currents necessary to neutralize the plasma injection payloads and those naturally occurring in the aurora could be responsible for the ions observed in the first two observations. Associated with the aurora, both bulk heating and tail heating are observed, sometimes simultaneously. In this case, either different masses are accelerated and/or different mechanisms are responsible. The bulk heating is closely correlated with the aurora structure while tail heating is not so well correlated. High-time-resolution rocket ion data have revealed that the transverse acceleration process is of very short duration (~100 ms) and occurs in a very limited volume (a few hundred kilometers along B and on the order of the ion gyrodiameter across B). Such impulse acceleration events are correlated with waves near the lower hybrid resonance. Wave injections of electromagnetic waves near the lower hybrid frequency result in the transverse acceleration of ambient ions     

Nuclear multifragmentation, percolation, and the fisher droplet model: common features of reducibility and thermal scaling

It is shown that the Fisher droplet model, percolation, and nuclear multifragmentation share the common features of reducibility (stochasticity in multiplicity distributions) and thermal scaling (one-fragment production probabilities are Boltzmann factors). Barriers obtained, for cluster production on percolation lattices, from the Boltzmann factors show a power-law dependence on cluster size with an exponent of 0.42+/-0.02. The EOS Collaboration Au multifragmentation data yield barriers with a power-law exponent of 0.68+/-0.03. Values of the surface energy coefficient of a low density nuclear system are also extracted.