Isomerization of a highly excited vibrational state of acetylene was studied using the Coulomb explosion imaging technique. A vinylidene isomer was prepared by electron photodetachment of the negative molecular ion and the corresponding distribution function of the nuclear configurations of the molecule was sampled after a time period of 3.5 ms. The population of the vinylidene isomer was found to be significantly high (ϳ50%), in contrast to the commonly accepted notion of vinylidene as a short-lived isomer. [S0031-9007(98)07417-1]

Energy loss in the MeV range of simple clusters impinging on thin carbon targets has been measured using a time-of-flight method. Stopping-power ratios defined as the ratio of the stopping power of the cluster to the sum of the stopping powers of the constituent atoms moving at the same velocity were investigated. Stoppingpower ratios close to unity were observed for O 2 and B 3 clusters, while deenhancement effect is observed in the stopping-power ratios of C 3 and C 4. The experimental results are compared both with an existing theoretical model, which takes into account the spatial correlation of the fragments, and with a simple united-atom model, which also includes the charge state evolution of the fragment ions inside the target.

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