Arnold van Wyk: Recently Published Works

Ferguson, Howard

doi:10.1017/s0040298200044673

Cited by 2 publications

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“…2 Figure 1 shows the gamma-ray decay schemes obtained principally from the Be 9 (He 3 ,/>y)B 11 reaction. In this set of experiments the gamma spectrum from each level was separated from the others by coincidences measured with the appropriate proton group.…”

Section: Gamma-ray Branching and Some Spinmentioning

confidence: 99%

Gamma-Ray Branching and Some Spin and Parity Assignments inB11

et al. 1958

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would be changed by about twice the quoted uncertainties. The values given should thus be regarded as uncertain to about this degree.In view of the necessary choice of weights for the various measurements of the proton gyromagnetic ratio and the preliminary nature of the present result, it does not seem desirable to calculate improved values for the atomic constants at this time. It is interesting to note, however, that the present value of the gyromagnetic ratio, when combined with the average of the available proton cyclotron resonance results, 13 gives a value for the Faraday which is about half-way between the values obtained from the iodine and the silver voltameters. 11 ' 12 A new complete adjustment of the constants should be delayed until a number of relevant experiments now under way are completed. At that time the value of the ampere as maintained by the national laboratories will probably be one of the quantities to be adjusted.We would like to express our thanks to the many people at NBS who have contributed to this experiment. In particular we would like to thank L. Costrell who designed the electronic apparatus and R. D. Cutkosky and L. M. Branscomb who collaborated on the early part of the experiment. We are very much indebted to the U. S. Coast and Geodetic Survey for permission to carry out the experiment at the Fredericksburg Magnetic Observatory, and to Mr. R. E. Gebhardt and the members of the Observatory staff for their active cooperation. We should also like to thank M. Packard and A. L. Bloom of Varian Associates for valuable information on freeprecession measurements in the earth's field. ! E. L. Hahn, Phys. iJev. 77, 297 (1950). 2 M. Packard and R. Varian, Phys. Rev. 93, 941 (1954). 3 N. Bloembergen and R. V. Pound, Phys. Rev. 9j>, 8 (1954). 4 P. L. Bender (to be published). 5 This solenoid has also been used in a recent determination of the ampere.

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Section: Gamma-ray Branching and Some Spinmentioning

confidence: 99%

Gamma-Ray Branching and Some Spin and Parity Assignments inB11

et al. 1958

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“…This combination provided good cutoff a t 3950 A. The relative quanta1 output of the hydrogen lamp was l;no\vrn a t each wavelength from 2500-3800 A in ternis of the luminescence of pure anthracene, u~hich is lcno~v~i to be collstallt over this region (3,4). T h e range was extended to 4100 -4 by calibrating tlie lanlp output against the luminescence intensity from a totally (99y0) absorbing solutioli of tetracene.…”

Section: E X P E R I M E N T a Lmentioning

confidence: 90%

The Luminescence of Complex Molecules in Relation to the Internal Conversion of Excitation Energy. Part I

Hochstrasser¹

1959

Can. J. Chem.

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The relative fluorescence yields of a variety of double molecules have been m e a s~~r e d as a function of the \vavelength of exciting light. I n some cases the yield from the second excited state is lower than from the first. This effect is attributed to either photodecomposition or to the enhancement of intramolec~~lar energy transfer processes which can compete with the internal conversion between the excited singlet states. The experiments on bianthrone have suggestecl a method of elucidating the mechanism of the photochromic iso~nerization of this compound. INTRODUCTIONThe fluorescelice of tlie vast majority of aromatic compounds arises from the radiative transition -first excited singlet to ground (singlet) state. On excitation to higher electronic states this same luminescence is observed and usually with unchanged yield. This implies that the rate of internal co~lversio~i to the radiating level is fast co~npared to the rate of intersystem crossing between upper excited states of different n~ultiplicity. I t has been suggested (3) that the fall-off in fluorescence yield of dibromoanthrace~ie excited with light below 3000 A is due to heavy atom-induced i~ltersystem crossing to the second triplet level. This indicates comparable rates for these co~npeting processes. Preliminary studies have indicated that a variety of molecules wliich are apparently quite stable photochemically have luminescence efficiencies wliich are anolllolous in ternis of the above rule.In this work the relative luminescence yields of a series of double molecules have been measured as a function of the exciting wavelength. A double molecule is one co~isisting of two identical parts coupled through a conjugating liillctge. E X P E R I M E N T A LThe fluorescence measurements were liiade by illuminating the samples contained in a Vycor tube or silica cell with the bean1 from a hydrogen lamp and Beck~lian D.U. monochromater. The luminescence was detected over a 20" region centering a t 70" to the main beam by liieans of an end-on-type pllotolnultiplier with S11 response. The incident radiation was filtered out by 1.5 c~i i of a saturated solution of sodium nitrite in water. By using suitable Corning filters, the cutoff could be extended to longer wavelengths. This combination provided good cutoff a t 3950 A. The relative quanta1 output of the hydrogen lamp was l;no\vrn a t each wavelength from 2500-3800 A in ternis of the luminescence of pure anthracene, u~hich is lcno~v~i to be collstallt over this region (3,4). T h e range was extended to 4100 -4 by calibrating tlie lanlp output against the luminescence intensity from a totally (99y0) absorbing solutioli of tetracene. The fluorescelice yield of tetracene is independent of the exciting light wavelength in this region of its absorption.The hydrogen lamp becornes less conti~iuous above 3700 A but good reproducibility could be obtained by opening up the mollochrolnater slit for this range of excitation. All the solutions urhich were studied absorbed a t least 99% of the incident li...

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Arnold van Wyk: Recently Published Works

Cited by 2 publications

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Gamma-Ray Branching and Some Spin and Parity Assignments inB11

Gamma-Ray Branching and Some Spin and Parity Assignments inB11

The Luminescence of Complex Molecules in Relation to the Internal Conversion of Excitation Energy. Part I

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