On the verge of Umdeutung in Minnesota: Van Vleck and the correspondence principle (Part One)

In October 1924, the Physical Review, a relatively minor journal at the time, published a remarkable two-part paper by John H. Van Vleck, working in virtual isolation at the University of Minnesota. Van Vleck combined advanced techniques of classical mechanics with Bohr's correspondence principle and Einstein's quantum theory of radiation to find quantum analogues of classical expressions for the emission, absorption, and dispersion of radiation. For modern readers Van Vleck's paper is much easier to follow than the famous paper by Kramers and Heisenberg on dispersion theory, which covers similar terrain and is widely credited to have led directly to Heisenberg's "Umdeutung" paper. This makes Van Vleck's paper extremely valuable for the reconstruction of the genesis of matrix mechanics. It also makes it tempting to ask why Van Vleck did not take the next step and develop matrix mechanics himself.Comment: 82 page

Deactivation processes in isolated aromatic heterocycles and pyrenes

In der vorliegenden Arbeit wurde erfolgreich eine neue Gasphasen-Apparatur für Photoelektronen-Imaging-Experimente simuliert, aufgebaut und in Verbindung mit einem ps-Lasersystem in Betrieb genommen. Neben dem Aufbau der Apparatur stand die Aufklärung der Dynamik angeregter Zustände von aromatischen Heterocyclen und Pyrenen im Fokus dieser Arbeit. Die untersuchten Moleküle wurden durch Resonanzverstärkte Mehrphotonenionisation in einem Molekularstrahlexperiment sowohl zeit-, als auch frequenzaufgelöst untersucht.In the presented work a new gas phase apparatus for photoelectron imaging experiments was succesfully simulated, constructed and together with a ps laser system put into operation. Besides the building of the new apparatus, the focus of this work was set to elucidate the excited state dynamics of selected aromatic heterocycles and pyrenes. The examined molecules were investigated by frequency- and time-resolved resonance enhanced multi photon ionisation spectroscopy using a molecular beam experiment