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We will present results of experiments that use intense few-cycle laser pulses with a known carrier-envelope phase on impulsively aligned polyatomic molecules to investigate the role of valence electron dynamics in bond-breaking processes. The experiments corroborate, that our recent discovery of a novel ionization-fragmentation mechanism, which puts a polyatomic molecule into a very high charge state of +12 and beyond already at very moderate laser intensities, and which leads to complete molecular decomposition with a concerted emission of all protons with high kinetic energies, is a multi-bond version of the well known enhanced-ionization mechanism. Furthermore, the experiments reveal a universal method to control molecular fragmentation and isomerization processes in polyatomic molecules that can be applied to a large class of molecules, despite the complexity of the many valence electrons and bonds in these systems. The method is based on a controlled population of excited electronic states on the natural, sub-femtosecond time-scale of the electrons, and exploits the dependence of the electron recollision energy on the carrier-envelope phase of few-cycle laser pulses in the well-known recollision mechanism of strong-field attosecond physics Our results give detailed insight into the role of the valence electrons in fragmentation and isomerization reactions in polyatomic molecules.
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