Mercury, atomic excitation

Frish and Kraulinya and, most recently, by Czajkowski, Skardis, and Krause [71] and Czajkowski, Krause and Skardis [96]. Frish and Bochkova [97, 98] studied excitation transfer from the 6 aPr and 6 aP0 mercury atoms excited by collisions with electrons in a discharge, to various states in sodium. Kraulinya [99] optically excited the Hg(6 aPJ state and followed the excitation transfer to sodium by monitoring the intensities of the collisionally sensitized sodium lines. Her results which are quoted within 30% — 50% are summarized in Table 4.5 and are compared with the cross sections determined by Czajkowski, Skardis and Krause [71], The considerable discrepancies between the two sets of results are apparently due to errors arising from the trapping of mercury resonance radiation [100, 28] which must have particularly affected Kraulinya s results, and from the uncertainty in the determination of the mercury and sodium vapor densities in the binary mixture. 

C15-0071. The light-emitting decay of excited mercury atoms is first order, with a rate constant of... 

In an effort to characterize the species formed in vapors containing mercury and arenes upon irradiation with UV light, the formation of exciplexes between excited mercury atoms and arenes has been investigated theoretically. For benzene, these investigations suggest the formation of an exciplex involving the Hg atom in the state and an 772-bound molecule of benzene. This loose complex (3[Hg(772-arene)] Figure 9) with estimated Flg-C bonds of 2.36A... 

Wrembel and Pajak [486] evaporated mercury from natural water samples with argon and amalgamated the mercury with a gold foil. The mercury was excited in a ring-discharge plasma and determined by atomic emission spectroscopy. The method was applied to the determination of mercury in seawater in the range 0.01-1.0 xg/l. 

Gray [215] studied the photooxidation of methane and ethane at room temperature in the gas phase using Hg as a photosensitizer. Hydroperoxide was found as the product of oxidation. Along with hydroperoxide, ozone was also found as the product of photooxidation. It was supposed to be due to the reaction of excited mercury atoms with dioxygen. 

The mercury lamp has been the conventional light source used in photochemistry. The ground-state mercury atom, Hg, has two electrons in its highest occupied orbital, the 6s atomic orbital. Excited mercury... 

One of the first applications of this chopped-beam irradiation technitriplet spectra was reported by Labhart From a knowledge of the intensity of the irradiation light, he determined the quantum yield of triplet generation to be 0.55 0.11 for outgassed solutions of 1,2-benzanthrazene in hexane at room temperature. Hunziker 32) has applied this method to the study of the gas-phase absorption spectrum of triplet naphthalene. A gas mixture of 500 torr Na, 0.3 mtorr Hg, and about 10 mtorr naphthalene was irradiated by a modulated low-pressure mercury lamp. The mercury vapor in the cell efficiently absorbed the line spectrum of the lamp and acted as a photosensitizer. The triplet state of naphthalene was formed directly through collisional deactivation of the excited mercury atoms. 

Recombination of fhe ionized elecfron wifh the argon cation produces an electronically excited argon atom, which can energize and subsequently ionize a mercury atom ... 

The electronically excited mercury atom generated by the recombination of the mercury cation with an electron loses its energy radiatively. The above are only a few of fhe processes fhaf fake place in the lamp, but the combined effect is the emission of light in the UV and visible regions and the generation of heat The heat vaporizes some of fhe mercury mefal. The mercury cations are conducting and the current passing across the electrodes rises until a steady state is reached. 

For example, 6 P, (six triplet P one) state of mercury signifies that the total energy of the state corresponds to n = 6 the orbital angular momentum is L— 1 the multiplicity is three hence it is a triplet energy state and the spins of the two valence electrons must be parallel (S = 1) and the particular value of 3 is 1 (/= 1). Since a normal mercury atom, has a pair of electrons with opposed spin in the S orbital, this must be an excited energy state, where a 6S electron is promoted to a 6P state. 

The quenching of resonance radiation of mercury from excited 6 state by large number of added gases has been studied. This state is populated through 63P1 61S0 transitions by mercury atoms and emits... 

A mechanism by which electronic energy is sometimes made available for chemical purposes is that which occurs in the so-called Stoss zweiter Art , or collision of the second kind . Cario and Franck found that on exposure of a mixture of mercury vapour and hydrogen to the mercury line 2536-7 A, the absorbed light stimulated the mercury atoms electronically, and that the excited mercury atoms were able on collision with hydrogen molecules to resolve them into atoms. The atomic hydrogen so produced was detected by its great chemical activity. A number of other examples of this phenomenon were found Z. Phyaik, 1922, 21, 161. 

Second, the oxygen can itself quench the excited mercury atom... 

Nonconjugated dienes and polyenes have triplet photochemistry which may be considered to arise from intramolecular interaction of one excited double bond with an isolated ground-state double bond. For example, the photocyclization of enrfo-dicyclopentadiene can be effected using acetone as a sensitizer.286 Other more flexible 1,5-dienes, when sensitized to triplet states, cross couple to yield bicyclo[2.1.1]-hexane structures. For instance, triplet mercury atoms convert both 1,5-hexadiene and 1,5-cyclooctadiene to such structures.267 Irradiation of the cyclooctadiene in the presence of cuprous chloride produces the tricyclo derivative in good yield266 but recent evidence again indicates that this latter reaction may proceed via free-radical intermediates.269... 

The excited mercury atom Hg can attack many different molecules, either by a direct chemical mechanism or by energy transfer. It will abstract the halogen atom from molecules like HC1... 

Dissociation of water can be sensitized by excited mercury atoms... 

Since monoisotopic photosensitization studies are usually carried out with substrates which react with the excited mercury atoms to form mercury compounds, it follows that mercury vapor is consumed in the course of the reaction and, therefore, experiments have to be carried out... 

Even when conditions can he found which result in a distribution of isotopes in upper states, different from that in AIIg a reaction is still required which fixes this upper state distribution as stable compounds of mercury. Therefore, a developer reaction is required, which usually involves substrate molecules which contain Cl, O, OH, etc. Such reactive fragments, however, react not only with excited, but also with ground-state mercury atoms. Isotopic fractionation will therefore occur only in an isotopieally-specific primary process of the type ... 

Any mechanism proposed for the detailed reaction path in the primary interaction of excited mercury atoms which 1T(T molecules and for the... 

In the second group of substrates, the quantum released by the excited mercury atom is either taken up by a strong bond, leading thereby to the formation of an excited molecule, as in the olefins, and perhaps also for the aldehydes and ketones ... 

The initial interaction of the excited mercury atom with the alkane molecule presumably takes the form of a slight overlap of the p-orbital of the 3Pi atom with the C-H sigma bond of the alkane molecule. In the formation of the cyclic intermediate (TS-2), the two hybrid sp-orbitals of mercury are very likely simultaneously involved through... 

Reactions sensitized by monatomic gases have been very extensively studied. The majority of the cases involve mercury vapor. Direct reaction of excited mercury atoms with other gases has also received considerable attention of late. 

If it is desired to calculate relative rates of the various reactions it now becomes necessary to evaluate [1Hg]. If the concentration of M can be maintained sufficiently high to prevent diffusion of radiation, i.e. if essentially every excited mercury atom collides effectively with a molecule M before it emits, and if the concentration of X can be kept so low that reactions between it and Hg may be neglected, the average rate of formation of excited mercury atoms per unit volume will be... 

An interesting case is the action of excited mercury on oxygen18 19. The energy required to dissociate the oxygen molecule is 5.13 electron volts or 118 kcal.mole-1. 63Pi mercury atoms are thus unable to cause this dissociation. However, the reaction... 

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