Mercury resonance radiation

Quenching crosssection of various gases for mercury resonance radiation... 

It may also be mentioned here that in specific molecular actions a particularly marked influence of like molecules upon one another is often to be observed. This is encountered in various ways in spectroscopy, in the extinction of the polarization of mercury resonance radiation with increasing vapour pressure, in the damping of fluorescence in concentrated solutions, and in various chemical reactions. As an example of the latter the decomposition of acetaldehyde (p. 70) may be quoted, where collisions between two molecules of the aldehyde are much more effective than collisions of aldehyde molecules with those of other gases. 

The formation of Hg(3Pi) atoms by absorption of mercury resonance radiation, 2537 A., and the following processes leading to water vapor... 

Gaviola and Wood have also shown that the fluorescence spectrum of both HgH and OH may be obtained from mixtures of mercury and water vapor irradiated with mercury resonance radiation, 2537 A. Beutler and Rabinowitch (15) considered this and the thermochemical values... 

Further information on this system is available from studies directed at photochemical isotope enrichment (16). In this work a mercury resonance lamp containing only Hg19S was used as a source. A flowing mixture of natural mercury and water vapor exposed to the Hg198 fine structure component of the mercury resonance radiation (2537 A.) was found to result in HgO considerably enriched in Hg198. It was concluded that this could only occur if Hg(3Pj) atoms reacted in a primary step to form either a compound which is removed from further contact with the reaction or which itself may react further but must not regenerate free Hg. Either reaction (55) or (56) would satisfy these conditions. If reaction (55) is the primary reaction, the further reaction... 

Apparently monochromatic resonance radiation of mercury which passes through mercury vapor at the saturated pressure at 25 °C is about half absorbed in four millimeters distance. Beer s law is not obeyed at all because the incident radiation cannot be considered to be actually monochromatic, and absorption coefficients of mercury vapor vary many times between zero and very high values in the very short space of one or two hundredths of an Angstrom unit. Moreover, absorption of mercury resonance radiation by mercury vapor is sufficiently great even at room temperature to make radiation imprisonment a very important phenomenon. If the reaction vessel has any dimension greater than a few millimeters the apparent mean life of Hg(63P ) may be several fold the true radiative life of 1.1 x 10"7 sec, reaction (27), because of multiple absorption and re-emission. 

Karl and Polanyi132 have described an experiment whereby the yield of vibrational energy in a quenching molecule was observed directly. Highly vibrationally excited CO was detected by infrared emission, in a mixture of mercury vapour and CO on irradiation with mercury resonance radiation. Evidently the processes... 

The exchange of electronic excitation between two atoms frequently results in sensitised fluorescence and one of the earlier examples was the discovery of emission of the fluorescence of atomic sodium, which occurs when a mixture of sodium and mercury vapour is irradiated with mercury resonance radiation at 2537 A... 

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. 

Smith32 reported that the absorbance of frozen cytosine solutions (0.5 mg/ml) decreased only 3-5% when irradiated with light from a mercury resonance lamp, but that the rate of loss of cytosine doubled when the frozen solution contained both cytosine and uracil. In solutions containing cytosine and thymine, a mixed dimer was apparently formed. Dried films of cytosine were apparently stable to the resonance radiation under conditions where there was 9% conversion of uracil and 17% conversion of thymine. There is a report that uracil dimer was formed in low yield in the photolysis of frozen cytosine solutions.32,81... 

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... 

Mercury Detection Instrument Use any suitable atomic absorption spectrophotometer equipped with a fast-response recorder and capable of measuring the radiation absorbed by mercury vapors at the mercury resonance line of 253.6 nm. A simple mercury vapor meter or detector equipped with a variable span recorder also is satisfactory. 

This chapter is intended to provide an overview of the results obtained from recent experimental studies of sensitized fluorescence and quenching of resonance radiation in alkali and mercury vapors, up to 1974. The many inconsistencies and discrepancies that still exist between experiment and theory as well as among the experimental results themselves, and that are a source of concern to those working in the field, will no doubt continue to be resolved as new ideas are put forward and as both theoretical and experimental techniques advance in precision and sophistication. 

For example, many authors profess to use the 2537 A. line of mercury. In most lamps this line is reversed and the radiation comes from the wings broadened to an extent dependent on the pressure and temperature in the lamp. A mercury resonance lamp, on the other hand, gives a... 

Sensitized Fluorescence. In this type of fluorescence, an atom emits radiation after collisional activation by a foreign atom that was excited previously by absorbing resonance radiation, but which has not yet been deactivated again. An example is the sensitized fluorescence of thallium atoms in a gas mixture containing a high pressure of mercury vapor and a low pressure of thallium vapor. When irradiated at the 253.65-nm mercury line, the thallium atoms emit at 377.57 and 535.05 nm. This type of fluorescence requires a higher concentration of foreign atoms than can be obtained in flame cells, but presumably it could be observed in nonflame cells. 

The first observation of non-radiative excitation energy transfer was made by Cario and Franck [126]. They investigated Hg and Th vapor and illuminated with the resonance line of mercury and found emission spectra from both atoms although Thallium did not absorb the light from the mercury resonance line. Since radiation by re-absorption was not possible, only a non-radiative energy transfer could have been operative with the Hg atoms as donor (sensitizer) and the Th atoms as acceptors. 

This chapter opens with an account of resonance fluorescence and its depolarization by external magnetic fields, a phenomenon now knovm as the Hanle effect. Experiments of this type in mercury vapour are described and we develop a classical theory to explain the shape of the observed signals. This is followed by a discussion of the applications of this technique to the accurate measurement of atomic lifetimes. For the sake of simplicity the effects of interatomic collisions and of trapping or reabsorption of resonance radiation in these experiments are not considered... 

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