State-resolved molecular beam experiments

More detailed insight into the energy exchange is obtained by the state-resolved molecular beam experiments [37]. As an example for these t) e of experiments. Fig. 3.10a shows TOF distributions from NO molecules in various rotational states (/") coming... 

S.D. Chao, S.A. Harich, D.X. Dai, C.C. Wang, X.M. Yang, R.T. Skodje, A fully state and angle resolved study of the H+HD D+H2 reaction Comparison of a molecular beam experiment to ab initio quantum reaction dynamics, J. Chem. Phys. 117 (2002) 8341. 

The development of the experimental techniques for the production of slow molecular beams described in Chapter 14 offers the unique possibility of studying state and angle-resolved differential scattering of molecules in the presence of external electromagnetic fields. Molecular beam experiments with Stark decelerated and guided molecular beams can be designed to probe fully state-resolved differential cross-sections (DCSs), which contain detailed information about the collision process. This... 

As already mentioned in Sect. 2.2.1.1 to perform a meaningful comparison with experimental results, both the rovibrational distribution and the energy width of the molecular beam have been taken into account [20], In order to do so, first the quantum monoenergetic state-resolved sticking probabilities, S v,J E), are computed for a large range of incidence energies and the rovibrational states populated in molecular beams experiments. These probabilities are used to compute the... 

Calculations using transition state theory (TST) are the subject of an other article (see Transition State Theory). This method gives rate constants for chemical reactions, but cannot normally give the energy resolved or quantum state-to-state detail that is needed for comparison with, for example, the results of molecular beam experiments. Sophisticated versions of transition state theory (that include, for example, variational placement of the transition state, optimum reaction paths for particular mass combinations, and tunneling corrections) have been applied to several reactions including those involving polyatomic molecules. Examples include ... 

The time-of-flight spectrum of the H-atom product from the H20 photodissociation at 157 nm was measured using the HRTOF technique described above. The experimental TOF spectrum is then converted into the total product translational distribution of the photodissociation products. Figure 5 shows the total product translational energy spectrum of H20 photodissociation at 157.6 nm in the molecular beam condition (with rotational temperature 10 K or less). Five vibrational features have been observed in each of this spectrum, which can be easily assigned to the vibrationally excited OH (v = 0 to 4) products from the photodissociation of H20 at 157.6 nm. In the experiment under the molecular beam condition, rotational structures with larger N quantum numbers are partially resolved. By integrating the whole area of each vibrational manifold, the OH vibrational state distribution from the H2O sample at 10 K can be obtained. In... 

Emission spectra of radical cations are obtained by vacuum UV ionization and subsequent laser excitation in noble-gas matrices (see below), or by electron-impact ionization of a beam of neutral parent molecules at energies above the first ionic excited state. After internal conversion to the first excited state, emission may compete more or less successfully with radiationless deactivation. If the experiment is carried out on a supersonic molecular beam one obtains highly resolved emission spectra which, in the case of small molecules, may contain sufficient information to allow a determination of the molecular structure. 

Theory quite naturally gives us the initial and final state resolved probabilities, but in experiment this is not always so. The internal state populations in a molecular beam are determined by the temperature of the nozzle used to produce the supersonic expansion. More than one state is present in such a beam. This has been partially overcome in recent years by Raman pumping of the incident molecular beam [66-69]. Laser beams intercept the molecular beam moving a fraction of the molecules into a particular ro-vibrational state (determined by the laser properties). With careful timing of the firing of the probe lasers, it is possible to measure changes in this fraction of molecules and measure some of the final states populated by the scattering process. 

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