Pulsed molecular beam reactive

Characterization and analysis are performed using the following surface science techniques temperature programmed desorption/reaction (TPD/TPR), pulsed molecular beam reactive scattering (pMBRS) (IRRAS), metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS) and auger electron spectroscopy (AES). First the experimental setup is briefly described, followed by the support preparation and characterization as well procedures utilized in this work. These descriptions include a concise introduction to the underlying physical principles of the applied techniques (including experimental details). 

Linear hydrocarbon radicals have been the subject of intensive laboratory spectroscopic and radio-astronomical research since the early 1980s. In recent years, a considerable number of rotational spectroscopic studies of medium to longer hydrocarbon chains such as C5H, CeH, CgH, and ChH have been carried out using a pulsed molecular beam FTMW spectrometer. The high resolution offered by such a spectrometer allowed the detection of the hyperfine sphtting of rotational transitions. These measurements improved fine and hyperfine coupling constants and provided rest frequencies with accuracies better than 0.30 km s in equivalent radial velocity up to 50 GHz. Indeed, some of the small C H radicals with n < 9 have subsequently been detected in space, in molecular cloud cores, and in certain circumstellar shells. These hydrocarbon chains are among the most abundant reactive space molecules known. 

Molecular Beam Reactive Scattering Using Pulsed Molecular Beams... 

Catalytic Reactivity. The size-dependent cluster catalysis was first studied by pulsed molecular beams. In these experiments, a nitric oxide molecular pulse is injected onto the cluster catalysts and the product molecules CO2 and N2 are quantitatively detected by a mass spectrometer as a function of cluster size, temperature, and CO background pressure [468]. The catal3dic formation of CO2 on Pdso and Pd is shown in Fig. 1.95a and b for selected temperatures and for a constant CO partial pressure of 5 x 10 mbar and an NO effective pressure of 1 x 10 mbar. The width of the NO pulse was 100 ms. Pdg and Pdgo show almost no catalytic reactivity up to about 390 K. For Pdso, maximal reactivity is observed at 420 K whereas Pdg is most reactive at 450 K. At higher temperatures, the formation of CO2 decreases. The CO2 formation on both cluster sizes at temperature of maximal reactivity is stable even after hundreds of NO pulses. 

Beyond straightforward studies of the real-time evolution of the neutral molecules and clusters, it should be possible to do things to the size-selected neutrals. They could be excited vibrationally or electronically by radiation, for example. Perhaps the most fascinating possibility of the NeNePo method would be, to study in real-time, reactive collisions of size-selected molecules and clusters with substances added to the interaction region of the laser pulses and molecular beam. 

Steady state has to be reached and this requirement is not necessarily fulfilled with pulsed beams of narrow temporal width. Also the laser beam section has to be greater than the reaction zone, indeed if it is smaller, molecules produced outside the irradiated volume and scattered into it are counted. Qearly in our case the product densities n(v ,K") in the irradiated volume are dependant on the outcome of previous outside reactive collisions. We have therefore developed a simple realistic model to evaluate the correction function defined by the spatial and temporal overlap of the molecular beams. 

---