Mercury excited states

In an atom of the second column of the periodic system, such as mercury, the two valence electrons are in the normal state s-electroiis, and form a completed sub-group. Two such atoms would hence interact in a way similar to two helium atoms the attractive forces would be at most very small. This is the case for Hg2, which in the normal state has an energy of dissociation of only 0.05 v.e. But if one or both of the atoms is excited strong attractive forces can arise and indeed the excited states of Hg2 are found to have energies of dissociation of about 1 v.e. 

The low solubility of fullerene (Ceo) in common organic solvents such as THE, MeCN and DCM interferes with its functionalization, which is a key step for its synthetic applications. Solid state photochemistry is a powerful strategy for overcoming this difficulty. Thus a 1 1 mixture of Cgo and 9-methylanthra-cene (Equation 4.10, R = Me) exposed to a high-pressure mercury lamp gives the adduct 72 (R = Me) with 68% conversion [51]. No 9-methylanthracene dimers were detected. Anthracene does not react with Ceo under these conditions this has been correlated to its ionization potential which is lower than that of the 9-methyl derivative. This suggests that the Diels-Alder reaction proceeds via photo-induced electron transfer from 9-methylanthracene to the triplet excited state of Ceo-... 

C07-0057. From Figure 7-14. calculate the energy difference in kilojoules per mole between the excited state of mercury that emits 404-nm light and the ground state. 

Franck and Gustav Hertz passed electrons through mercury vapor at low pressure to determine the minimum kinetic energy required to produce the excited state that emits ultraviolet light at 253.7 nm. What is that minimum kinetic energy What wavelength is associated with electrons of this energy ... 

The first Mossbauer measurements involving mercury isotopes were reported by Carlson and Temperley [481], in 1969. They observed the resonance absorption of the 32.2 keV y-transition in (Fig. 7.87). The experiment was performed with zero velocity by comparing the detector counts at 70 K with those registered at 300 K. The short half-life of the excited state (0.2 ns) leads to a natural line width of 43 mm s Furthermore, the internal conversion coefficient is very large (cc = 39) and the oi pj precursor populates the 32 keV Mossbauer level very inefficiently ( 10%). 

By media variables we mean the solvent, electrolyte, and electrodes employed in electrochemical generation of excited states. The roles which these play in the emissive process have not been sufficiently investigated. The combination of A vV-dimethylformamide, or acetonitrile, tetra-n-butylammonium perchlorate and platinum have been most commonly reported because they have been found empirically to function well. Despite various inadequacies of these systems, however, relatively little has been done to find and develop improved conditions under which emission could be seen and studied. Electrochemiluminescence emission has also been observed in dimethyl sulfite, propylene carbonate, 1,2-dimethoxyethane, trimethylacetonitrile, and benzonitrile.17 Recently the last of these has proven very useful for stabilizing the rubrene cation radical.65,66 Other electrolytes that have been tried are tetraethylam-monium bromide and perchlorate1 and tetra-n-butylammonium bromide and iodide.5 Emission has also been observed with gold,4 mercury,5 and transparent tin oxide electrodes,9 but few studies have yet been made1 as to the effects of electrode construction and orientation on the emission character. 

Emission spectrum Radiation from an atom in an excited state, usually displayed as radiant power vs. wavelength. Each atom or molecule has a unique spectrum. The spectra can be observed as narrow line emission (atomic emission spectra) or as quasi-continuous emissions (molecular emission spectra). A mercury plasma emits both line spectra and continuous spectra simultaneously. 

Furans are able to undergo photocycloaddition of the [W2S+ 2S] and the [W4S+ 4S] type to suitable substrates. With benzene (80JCS(P1)2174) five 1 1 products are obtained. The relative proportions of these products are highly variable and depend on the relative concentration of the reactants, the irradiation time, the light intensity and the temperature of the solution. For the shortest irradiation time with a low-pressure mercury lamp at 15 °C, the relative proportions are 1 1 10 40 2. The major product is the 2,5 l, 4 -adduct (301) and the next most prolific is the 2,3 l, 2 -adduct (302). Adduct (301) is unreactive to dienophiles but gives adduct (302) by Cope reaction at 60-70 °C. This reaction can also be achieved by irradiation of a cyclohexane solution of (301). Adduct (302) reacts readily with dienophiles in ethereal solution to form Diels-Alder adducts. The minor adducts possess structures (303), (304) and (305). The reaction is thought to involve the first excited triplet of benzene or an excited state complex. A [ .4s+ .4g] photoadduct (306) is formed... 

The atoms of mercury and of cadmium provide many examples of such reactions, though they are not the only ones. The most important processes of this type involve excited mercury Hg, this label hiding the fact that there are several different excited states in this atom. (The population of these states depends on the pressure see Chapter 7 about the Hg arc emissions.) In the gas phase, Hg will attack organic molecules such as hydrocarbons through a reaction of hydrogen abstraction... 

The critical property of the Mercat process [3-8] that gives it its selectivity is that only Hg atoms in the vapor phase undergo reaction, because their absorption line is narrow and matched with the sharp emission line of the lamp. Mercury dissolved in the liquid phase has a broadened and shifted absorption band and Hg in solution has a short excited-state lifetime, so the liquid phase undergoes no significant reaction. In the vapor, Eqs. (2)—(5) produce the dehydro dimer, which condenses. 

Dehydrodimerization. On excitation with a mercury vapor lamp, mercury is converted to an excited state, Hg, which can convert a C—H bond into a carbon radical and a hydrogen atom. This process can result in dehydrodimerization, which has been known for some time, but which has not been synthetically useful because of low yields when carried out in solution. Brown and Crabtree1 have shown that this reaction can be synthetically useful when carried out in the vapor phase, in which the reaction is much faster than in a liquid phase, and in which very high selectivities are attainable. Secondary C—H bonds are cleaved more readily than primary ones, and tertiary C—H bonds are cleaved the most readily. Isobutane is dimerized exclusively to 2,2,3,3-tetramethylbutane. This dehydrodimerization is also applicable to alcohols, ethers, and silanes. Cross-dehydrodimerization is also possible, and is a useful synthetic reaction. 

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