Rydberg tagging

The so-called Rydberg tagging technique provides a quite dramatic improvement in resolution, particularly for hydrides. With this technique, rather than immediately photoionizing the recoiling H atoms they are excited to a high-n Rydberg state, in two steps, i.e. 

Laser Chemistry Spectroscopy, Dynamics and Applications Helmut H. TeUe, Angel Gonzalez Urena Robert J. Donovan 2007 John Wiley Sons, Ltd ISBN 978-0-471-48570-4 (HB) ISBN 978-0-471-48571-1 (PB) 

CH17 PHOTODISSOCIAHON OF LARGER POLYATOMIC MOLECULES ENERGY LANDSCAPES 

However, this turns out to be a rather complex dissociation process, as there are two competing mechanisms and several electronic states are involved. 

Theory shows that, in the most complex of the two mechanisms, the initially excited Si state reaches the dissociation asymptote, as a result of sequential non-adibatic couplings, via the Ta, T2, and Ti PESs. Further details can be found in the work of Mordaunt et al. (1998). 

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The title reaction was studied by the Doppler-selected TOF technique to be compared with Schnieder s results65 recorded by the Rydberg tagging... 

Compared to the H-atom Rydberg tagging technique,65 the resolution of the present method is somewhat worse, by about a factor of two. This loss in resolution, however, is realized in general only for photodissociation studies. In a typical crossed beam experiment, the product translational energy resolution is usually limited by the energy spread of the initial collision energy rather than the detection scheme. On the other hand, the present... 

In this chapter, we will describe the most recent advances made in our laboratory on the unimolecular dissociation of the important H2O molecule as well as the bimolecular reactions, 0(1D) + H2 —> OH + H and H + HD — H2 + D, using the H-atom Rydberg tagging TOF technique. Through these studies, detailed dynamical information can be extracted experimentally for these important systems. 

Fig. 1. Detection schemes for H-atoms. Rydberg tagging technique is slightly different from the (1 + l )-REMPI detection scheme in which the H atom is directly ionized Rydberg tagging only pumps the H atom to a high Rydberg state.

H2 molecular beam. The H-atom products were detected by the Rydberg tagging TOF technique using the same scheme described in the last paragraph with a rotatable MCP detector. Figure 4 shows the experimental scheme of the crossed beam setup for the 0(1D) + H2 reactive scattering studies. The scheme used for the H + D2(HD) studies is very similar to that used in the 0(1D) + H2 except that the H-atom beam source is generated from HI photodissociation rather than the 0(1D)-atom beam source from 02 photodissociation. 

The 0(1D) + HD reaction was also studied using the same Rydberg tagging TOF technique described above. The experiment was carried out at a collision energy of 1.7kcal/mol, which is below the 1.8 kcal/mol barrier for the abstraction mechanism inferred from previous experimental studies.63 The purpose of this experimental study is to investigate the isotope effect on this reaction. 

The more recent development of Rydberg tagging came about following collaboration between my colleague Michael Ashfold and Karl Welge in Bielefeld. One of the photofragments, H-atoms in the... 

On the experimental side, the coupling of crossed molecular beam techniciues with sophisticated detection techniques (Laser Induced Fluorescence, CARS or REMPI spectroscopy, Rydberg tagging photoionisation using synchrotron radiation or U lasers) has improved considerably the detailed study of chemicid reactivity. It is now possible to prepare reactants in a well defined state and to analyze the reaction products at a fixed scattering angle for a. collision at a well defined kinetic energy [1]. 

Finally, it is only right that we conclude this chapter with a further mention of the group that first demonstrated the virtues of the H-atom photofragment translational spectroscopy technique. Over the past few years, Welge, Schnieder, and co-workers [391,392] have concentrated much of their efforts on applying the same Rydberg tagging schemes to the... 

Using the H-atom Rydberg tagging time-of-flight crossed molecular beam technique, Dr. Ren studied the reaction resonance and non-adiabatic effects at a full quantum resolved level in the F + H2 system. Through state-to-state resolved experiments, he provided the first conclusive evidence of reaction resonances in the F %,2) + H2 -> HF + H reaction. The dramatic difference between the dynamics for the F( P3/2) + H2(j = 0,1) reactions represents a textbook example of the role of reactant rotational level in resonance phenomena in this benchmark system. Dr. Ren has also carried out a very high-resolution experimental study on the dynamics of the isotope substituted reaction, F( P3/2) -I- HD -> HF -I- D, with spectroscopic accuracy (a few cm ). These findings provided a very clear physical picture for reaction resonances in this benchmark system, which has eluded us for more than 30 years. 

This thesis will be organized as follows The Chap. 2 describes the H atom Rydberg tagging time-of-flight crossed molecular beam apparatus and experimental methods in our laboratory the Chap. 3 shows the research of resonance phenomenon in the F -I- H2 reaction in the Chap. 4, the breakdown of the B-O approximation in the F - - H2 reaction is introduced. 

Hydrogen Atom Rydberg Tagging Time-of-Flight Crossed Molecular Beam Apparatus... 

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