Principles of the Experiment

The three sublevels of Ti are split even in the absence of a magnetic field owing to the anisotropic dipolar interaction of the two unpaired electron spins. The sub-levels are labelled 2T), T , and jZ) and are related to the principal axis of the fine-structure tensor, which by symmetry are constrained to lie parallel to the three twofold symmetry axes of pentacene. The zero-field splitting in the case of pentacene is in the order of 1.5 GHz [14]. 

F ure 2. Schematic representation of the ODMR effect on a single molecule. Part (a) of the figure shows the five-level scheme relevant for the experiment. k 2 denote the population rates of the sublevels Uy U = X. Y. Z) and represent the depopulation rates. The relative magnitudes of the rates with respect to each other are indicated by the thickness of the arrows. Part (b) depicts the temporal evolution of the photon electron pulses as they are created by the detection system. Upon irradiation with microwaves in resonance with the T - Z transition the dark periods between the photon bunches are lengthened. 

Important for the detectability of a resonant microwave transition is the signal-to-noise ratio S/N. It is well known, that Rayleigh scattering is the limiting noise factor in single-molecule spectroscopy [16]. Both depend on the laser intensity. The S/N ratio can be approximated by 

Two different experimental arrangements have been successfully utilized for magnetic resonance experiments on single molecular spins [18, 19]. As in the optical single-molecule experiments the essential ingredients are a narrow-band laser, an efficient collection of the emitted fluorescence and a small excitation volume of the sample. To achieve a small sample volume the incoming laser light is either focussed 

For FDMR experiments it is desirable to be able to apply an external magnetic field. In one of the arrangements the field is provided by a pair of Helmholtz coils outside the cryostat which can be rotated with respect to the sample to obtain the directions of the principal axes of the zero-field tensor. With this approach the exciting laser can be kept focussed on the same sample volume while orienting the field, but the fields are limited to lOmT. In the other set-up the sample holder is inserted into the bore of a fixed superconducting Helmholtz-type magnet immersed in liquid helium. This allows the application of fields up to 1.3 T, but the direction of the magnetic field with respect to the zero-field tensor cannot be varied. 

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It is often inconvenient and/or experimentally impossible to coat the walls of the flow tube with the condensed phase, e.g., for horizontally mounted flow tubes. In this case, the liquid can be held in a rectangular container on the bottom of the flow tube. While the principle of the experiment is the same, corrections for only a portion of the surface area being reactive must be made. The same approach has been applied to studying the reactions of gases with solids. If the solid sample is in the form of a powder, there are usually multilayers of the crystalline grains in the sample container, which makes determination of the effective surface area available for reaction much more complex. For some typical applications of flow tubes to studying... 

The principle of the experiment is as follows a first pump pulse at 400 nm (Pump4oo) excites the electron donor (Pe) into its Si electronic state. After a variable time delay Ati (up to 1 ns) a conventionnal pump-probe measurement is performed at 530 nm (Pumps3o and Probes3o) on the ensuing transient species (Fig. lb). It allows us to determine the GSR dynamics of the Pe + cation upon excitation in its Do - Ds absorption band as a function of time delay after phototriggering the charge transfer reaction, i.e. as a function of the age of the transient. 

Measurements of daPs/dQ for positron-argon scattering have also been made by Finch et al. (1996a, b) and Falke et al. (1995, 1997) and for positron-krypton scattering by Falke et al. (1997). The principle of the experiments, involving the detection of the positronium in coincidence with an atomic ion, is illustrated schematically in Figure 4.28. More details of the system used by Finch et al. (1996a), which has also been used to study the differential ionization cross section, can be found in section 5.6. 

The basic principle of the experiment of Canter, Mills and Berko (1975) was to collide low energy positrons with a surface and to look for coincidence between a Lyman-a photon and a delayed gamma-ray arising from the subsequent annihilation of a 13S positronium. The presence of the Lyman-a signal was verified by the use of three interference filters with pass bands centred on, just above, and just below, 243 nm. An enhanced coincidence rate was found with the 243 nm filter in place. A similar Lyman-a gamma-ray technique has been adopted by all subsequent workers in this field (e.g. Laricchia et al., 1985 Hatamian, Conti and Rich, 1987 Ley et al., 1990 Schoepf et al., 1992 Steiger and Conti, 1992 Hagena et al., 1993 Day, Charlton and Laricchia, 2000). 

This paper presents the first experimental results for the solid motion inside a pilot-scale rotary kiln. Such data are useful to enable efficient pyrolysis reactions inside a rotary kiln to be carried out, through the prediction of residence time and material hold-up, and the evaluation of different surfaces and temperature profiles according to the operating conditions. In the first part, the pilot-scale rotary kiln and the principle of the experiments will be described. An original dynamic solid motion model will be presented in the second part, this dynamic model is derived from the original static model of Seaman [1], The static and dynamic experimental results are finally compared with the simulated results. 

Fig.l. Principle of the experiment. The low field seeking atoms are driven to the B—field minimum. The gas is studied by-observing the atoms that escape the trap after relaxation... 

The principle of the experiment is to see an increase in the intensity due to laser-stimulated transitions when negative muons are stopped in the helium gas present in a multipass optical cavity, where a high-density electromagnetic radiation of the correct wavelength is stored it is crucial here that the lifetimes of the levels in which one is interested are around 10 12 s (we recall that the negative muon cascade time is about 1 ns or less). 

The principle of the experiment is illustrated by Fig. 12. On the left-hand side the absorption band of an inhomogeneously broadened transition, e.g., the OH-stretching band in different H-bonded local environments, is depicted schematically. Structures with different OH-O bond angles and/or 0-0 bond lengths show up in the spectrum with different OH frequencies linear bonds and shorter bond length correspond to larger red shifts... 

The principle of the experiment is to record the reaction signal (e.g., a chemiluminescence signal) as a function of the average number and to fit it by a Poisson distribution or by a linear combination of Poisson distributions. The order of the Poisson distribution which best fits the experimental data is a direct measure of the exact number of reactants involved in the chemical process under study, since the reactants are confined on a cluster of finite size. For instance, if the reaction signal is well fitted by the Poisson distribution P2 (jn)), when varying the average... 

A description of these methods has been given by Boutin [22] and we shall merely remind the basic principles of the experiments. 

The main part of the book is concerned with the post-war work on Lamb shifts. The theoretical chapter is intended for non-specialists, but workers in the field may find it useful to have the formulae collected together with a consistent notation. On the experimental side, techniques have been so diverse that to have described them all in detail would have been to risk losing the thread of the thesis. I have aimed to explain the principles of the experiments, except in the case of hyperfine structures where I have used measurements without describing their experimental basis. 

The following so-called dynamic capillary method was developed by Van Hunsel Joos (1987b) and complements the area of application with respect to other methods. This method allows measurements from 50 ms up about 1 s, similar to the inclined plate and growing drop techniques described above, and can be used at liquid/liquid and liquid/gas interfaces without modification. The principle of the experiment is schematically given in Fig. 5.23. Two fluids are contained in a tube of diameter R. The interface (or surface in case of studies at the water/air interface) is located in such a way that its interfacial tension can be measured by the capillary rise of the lower liquid in a narrow capillary c, which connects the both fluids. The height of the capillary rise h is determined via a cathetometer Cat. 

The principle of the experiment is shown in Fig. 6.5. A small air bubble is formed at the tip of a capillary which is immersed in the solution. Via an electrodynamic excitation system and a membrane, a gas volume directly connected with the capillary is excited to harmonic oscillations. From the excitation voltage of the system in dependence on frequency, while keeping the bubble oscillation amplitude constant, the dilational elasticity and the exchange of matter can be calculated. The comparatively complex theory for data interpretation was described recently by Wantke et al. (1980, 1993). The method can be applied in a frequency interval from 5 Hz up to about 150 Hz. 

Here, G is a lattice vector in the reciprocal-space lattice. Fig. 5.7 illustrates the principle of the experiment in reciprocal space. Only when Eqns. (5.2) and (5.3) are simultaneously fulfiUed is there a finite intensity of the inelastically-scattered neutron wave. The observable quantity in the experiment is the intensity of the scattered neutron wave as a function of the energy loss and of the scattering vector... 

Figure 5.1 shows the principle of the experiment. Cluster ions are produced, thermalized and mass-selected in a first time-of-flight mass spectrometer. A packet of clusters of one size is irradiated with photons of variable energy. These induce an electronic transition which decays rapidly into vibrational excitation. If the cluster is small or hot enough the increase in the cluster temperature (ST) is sufficient to evaporate at least one atom. The overall process studied can thus be written ... 

The Stanford group was the first to perform in-beam Mossbauer experiments on Fe. The principle of the experiment is to excite stable Fe atoms from their ground... 

A new experimental procedure based on the isothermal desorption of vapour is proposed to extend the domain of characterisation of porous solids and powders by capillary condensation until the macropore range. The set-up is based on the use of a Tian-Calvet type microcalorimeter that insures a lull control of temperature gradients around the sample and allows the desorption isotherm to be determined very close to the saturation pressure. The principle of the experiment is described and the first results obtained for water desorption are compared to measurements based on gravimetry as well as to pore size distributions obtained by mercury porosimetry. 

Consider the principle of the experiment depicted in Figure 14.1. The porous medium, whose properties (grain sizes and porosity) are homogeneous in space, is bounded by two planes perpendicular to the Oz axis. The thickness of the layer is denoted by L. The material is immersed in a fluid, which saturates the interior of the porous medium. 

In the alternating airflow method, a piston is used to generate a low frequency alternating airflow through the test specimen and a condenser microphone is used to obtain the root mean square (rms) value of the pressure change in front of the porous material. Fig. 5.2 shows the basic principle of the experiment setup. 

State. The principle of the experiments is that since both oxygens of the carboxy-group are co-ordinated to cobalt atoms, they are not available for adjacent attack by the reductant hence various kinds of remote attack are favoured. The complexes (23 R= CH2CO2H or CMe2COaH) react with Cr according to the rate law (69). ... 

An elegant example of a surface-ahgned reaction is the oxidation of CO with O atoms produced by photodissociation of O2 when both reactants are localized parallel to step sites on a Pt surface. CO molecules absorbed on terraces of the same surface are less than half as reactive. The principle of the experiment and the results of probing the CO reactant before and after irradiation are shown in Figure 12.9. 

Experimentally, the diffusion coefficient is measmed by quasi-eleastic light scattering experiments (QELS). We recall the principle of the experiment. In semi-dilute solutions or gels, the polarized quasi-elastic light scattering is due to the local concentration fluctuations of the polymer. At a scattering angle 6, the autocorrelation function of the scattered electric field is >... 

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