State-altering experiment

Assumption of controlled change of the system characteristics during an experiment a state-altering experiment. 

The unique mechanical and structural properties of crystals necessitate the application of special experimental methods for the investigation of thd chemical kinetics of solids. In principle, all the physical parameters of substances involved in a chemical process can be used to follow the kinetics. These processes normally occur at high temperatures since they need thermal activation. Conventionally, the outcome of a solid state reaction experiment is inspected only after quenching. However, the quenching process is prone to alter many properties of the system, which explains the ambiguous results often found in the studies of solid state kinetics. 

Under the influence of low dosages of psycholytic agents, a peculiar distancing enables the patient, 05 the reflective core of the self, to observe the altered state. This assures continuous understanding by the patient of the artificial cause of his altered state of experience. 

Interrogative kinetics involves two types of experiments that are performed in sequence to reveal complex mechanisms and structure-activity relationships. The first type is a "state-defining" experiment that does not significantly perturb the lanetic state of the catalyst, but provides information that can characterize the state. The second type is a "state-altering" (typical) experiment that perturbs the catalyst and changes its composition or structure in some predetermined fashion. To complete the sequence another state-defining experiment is performed to characterize the new state of the catalyst. 

The principle of the ENDOR method is illustrated in Fig. 1. It refers to the most simple spin system with an electron spin S = 1/2 and a nuclear spin 1 = 1/2 for which an isotropic hf interaction, ajso, is considered. In a steady state ENDOR experiment an EPR transition (A, D), called the observer, is partly saturated by microwave radiation of amplitude Bi while a driving rf field of amplitude B2, called the pump, induces nuclear transitions. At frequencies vi and V2, the rf field tends to equalize the populations within the m,-states. This alters the degree of saturation of the observer so that, in the display of the EPR signal height versus the radio frequency, two ENDOR lines at transition frequencies vi = ajjo/2 - v (A, B) and V2 = z J2 + v (C, D) will be observed (v = / NSnBo denotes the nuclear Zeeman firequency for a static field Bo). 

It is not certain whether Sir Humphrey Davy (Fig. 1-7) knew of these considerations. He accepted a commission from the Admiralty for the protection of copper-clad wooden ships, which had been introduced in 1761. During his numerous laboratory experiments, he discovered the cathodic protection of copper by zinc or iron [3]. Davy had already put forward the hypothesis in 1812 that chemical and electrical changes are identical or at least arise from the same material property. He believed that chemical reaction forces could be reduced or increased by altering the electric state of the material. Materials can combine only if they have different electric charges. If an originally positive material can be artificially negatively... 

Unlike traditional surface science techniques (e.g., XPS, AES, and SIMS), EXAFS experiments do not routinely require ultrahigh vacuum equipment or electron- and ion-beam sources. Ultrahigh vacuum treatments and particle bombardment may alter the properties of the material under investigation. This is particularly important for accurate valence state determinations of transition metal elements that are susceptible to electron- and ion-beam reactions. Nevertheless, it is always more convenient to conduct experiments in one s own laboratory than at a Synchrotron radiation focility, which is therefore a significant drawback to the EXAFS technique. These focilities seldom provide timely access to beam lines for experimentation of a proprietary nature, and the logistical problems can be overwhelming. 

In a conventional Fe Mossbauer experiment with a powder sample, one would observe a so-called quadrupole doublet with two resonance lines of equal intensities. The separation of the lines, as given by (4.36), represents the quadrupole splitting The parameter Afg is of immense importance for chemical applications of the Mossbauer effect. It provides information about bond properties and local symmetry of the iron site. Since the quadrupole interaction does not alter the mean energy of the nuclear ground and excited states, the isomer shift S can also be derived from the spectrum it is given by the shift of the center of the quadrupole spectrum from zero velocity. 

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