Bulb experiment

In general one requires that gas and surface be equilibrated, such that they are at the same temperature. This may be a problem at loiv pressures, ivhere the gas molecules collide more often ivith the walls of the vacuum vessel than with the surface under study. Reducing the volume and increasing the pressure to the millibar regime by adding an inert gas helps to establish a region around the crystal where the gas is in thermal equilibrium with the surface. Such measurements are commonly referred to as bulb experiments. 

It is easy to conclude that activated CH4 dissociation on Ni(100) (and other transition metals) is dominated by direct rather than precursor-mediated processes under molecular beam conditions because of the strong dependence of S on Et and Tv. However, it is not as easy to decide in thermal bulb experiments and there has been considerable controversy over which dominates the thermal CH4 dissociation [59,285,286]. This is especially true since both lattice coupling in direct dissociation and a precursor-mediated dissociation with Ec>Ed (see Section 2.3.2) can cause k(Tg = 300K, Ts) to increase with Ts. One way to distinguish between these two possibilities is to compare isothermal rates k(T = Ts) with non-isothermal... 

In addition to molecular beam experiments, bulb experiments of methane on Ir(l 1 0)/Ir(l 1 1) were conducted in an attempt to determine the degree of contributions from the trapping-mediated and... 

Values ofS0,t determined experimentally from bulb experiments and those determined from calculations using molecular beam data atrg = 300 K. Also included, are calculated contributions toSG from the trapping mediated and direct mechanisms for methane dissociation on Ir(l 1 0)-(l x 2). 

The picosecond bulb experiments of Yoshihara and co-workers do not reveal a significant isotope effect on the threshold energy or the excess energy dependence of the channel three decay. See D. V. O Conner, M Sumitani, Y. Takagi, N. Nakashima, K. Kamogawa, Y. Udagawa, and K. Yoshihara, Chem. Phys., 93, 373 (1985). 

State selection by optical methods is a general and versatile tool which is applicable to the preparation of specific radiating and nonradiating states in both beam and bulb experiments [32-35]. This technique can be used both to prepare excited levels by direct excitation or to deplete a selected nonradiating level by optical pumping. The latter has been employed to study spin-orbit effects in... 

Reactions studied using the chemical activation technique in beam or bulb experiments yield important Information because the intermediate radicals have well-defined excitation energies unimolecular decompositions involving the formation of a C-F bond have additional appeal because many competing channels for decomposition open up and studies of branching ratios for C-H,... 

Molecular beam and bulb experiments have two goals. First, reaction cross sections can be transformed into reaction rate constants, which provide important kinetic information regarding chemical reaction rates. The rate constant with reactant state selection may be particularly important for technological applications. Indeed, a chemical mixture which reacts exothermically from one reactant state, and is inert from all other reactant states might provide a useful energy source to complement fossil fuels. For more fundamental reasons, we focus on the initial state selected rate constant for the D+H2 —> DH+H reaction in Chapter 5. 

Finally, there is a chemical activation gas bulb experiment from which it has been deduced that complete energy redistribution is very rapid in sec-butyl radicals excited above the unimolecular dissociation threshold-In these experiments H atoms add to cis-2-butene to produce vibrationally excited sec-butyl radicals... 

Tesla accepted an offer of land and free electricity in Colorado Springs by the local electrical company to continue his research. In 1899, he conducted experiments he considered to be of extreme importance in the conduction of electricity through the earth without the use of wires. He reported that he was able, by means of this principle, to illuminate electric light-bulbs twenty-six miles from the power source. This transmission mechanism, which Tesla explained as... 

We could explain the results of this experiment die way we did before die final distribution is clearly much more probable than the initial distribution. There is, however, another useful way of looking at this process. The system has gone from a highly ordered state (all the H2 molecules on the left, all the N2 molecules on the right) to a more disordered, or random, state in which the molecules are distributed evenly between the two bulbs. The same situation holds when marbles rather than molecules are mixed (Figure 17.3). In general, nature tends to move spontaneously from more ordered to more random states. 

Let us examine a chemical reaction to see if these same conditions apply. Suppose we fill two identical bulbs to equal pressures of nitrogen dioxide. Now immerse the first bulb (bulb A) in an ice bath and the second bulb (bulb B) in boiling water, as in Figure 9-4. The gas in bulb A at 0°C is almost colorless the gas in bulb B at 100°C is reddish-brown. The predominant molecular species in the cold bulb must be different from that in the hot bulb. A variety of experiments shows that the cold bulb contains mostly N204 molecules. These same experiments show that the hot bulb contains mostly NOa molecules. The N20 molecules absorb no visible light, so... 

Irradiation Procedure. Reaction mixtures were prepared at room temperature by transferring desired quantities of reactants from their storage bulbs to the reaction vessel, a 500-cc. spherical borosilicate glass flask attached to the vacuum line by a section of glass capillary tubing and a 4-mm. bore threaded glass valve with a Teflon plug (Fischer and Porter 795-609). Prior to each experiment this vessel was baked under vacuum at 500°C. for 12 or more hours. 

The requirements regarding commodities which are difficult to analyze are also not very clear. The listed crops do not cause difficulties in each kind of determination [e.g., brassica or bulb vegetables in gas chromatography/mass spectrometry (GC/MS)]. On the other hand, different species of the same crop may have different interference peaks, which may or may not affect quantitation. Presumably, the easiest approach is to perform additional validations, even if the final extracts are not difficult to analyze. In the author s experience, validations should generally include hops and tobacco, if the pesticide is used in these crops. 

Incandescent lamps consist of glass bulbs that enclose an electrically heated filament that emits light. For over 50 years prior to Thomas Edison s success, scientists had experimented with developing electric lamps. With financiers such as J. P. Morgan and the Vanderbilts, Edison founded the Edison Electric Light Company in 1878 with the prime mission to generate cheap electric power to provide an illumination source. For the filament of his electric lamp, Edison reportedly experimented on 6000 different types of materials, eventually narrowing his focus on fine platinum wire and a mix of 10% iridium with platinum. Unfortunately,... 

In a typical experiment, a 12.18-mmol sample of hydrogen chloride is frozen into a 500-ml. reaction bulb on the vacuum system. (Liquid nitrogen is the refrigerant.) An 8.22-mmol sample of (dimethylamino)difluorophosphine is then frozen into the bulb, the stopcock to the bulb is closed, and the system is allowed to warm slowly to 25°. Reaction is indi-... 

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