![]() ![]() As with the well-known case of azulene, this phenomenon appears to be associated with a large energy gap between the Sland S, states, and the absence of any efficient radiationless transformations of the S2 state. The fluorescence from S, thiophosgene has the remarkably high quantum yield of 0.7. The growing list of molecules showing fluorescence from S2states now includes thiophosgene and various other thiocarbonyl compounds (Levine, de Mayo) and 1,2-benzanthracene (Nickel). Birks has emphasized the precautions which are necessary to eliminate errors in the measurement of molecular fluorescence parameters of aromatic molecules, for example those due to self-quenching, and has questioned the accuracy of many published data. There has been considerably increased experimental and theoretical interest in two-photon processes during the year from a number of groups, and Swofford and McClain have given a full description of a two-photon excitation spectrometer. Correction for such effects may sometimes be necessary. One may also note the important survey of effects of polarization in fluorescence measurements presented by Cehelnik and his co-workers. Calculations on NH and CH2 have led Colbourn to question the normal assumption that electrons in triplet species are more widely separated than in the corresponding singlets. This appears to avoid some of the difficulties recently recognized in the conventional basis of these rules. On the theoretical and spectroscopic side of the subject, one of the more interesting developments during the year has been the reformulation by Colpa on a strict SCF approximation of Hund’s rules for predicting the ordering of electronic states. We hope, however, that the general quality has not suffered unduly but we shall as always be grateful to receive any comments from readers which may help us to preserve or improve the quality of the presentation and the critical content without adding to the length. Some Reporters have found this restriction more irksome than others. This is the first Volume of ‘Photochemistry’ to suffer the general restriction on length which the Chemical Society has been obliged for economic reasons to apply to all Specialist Periodical Reports. In Volume 7 we retain essentially the same layout as in Volume 6, except that the Chapter on Developments in Instrumentation and Techniques is being deferred until Volume 8 where it will form part of a biennial review of this area. at The Stonebridge Press, Bristol BS4 5NU Organic formulae composed by Wright's Symbolset method Printed in Great Britain by John Wright and Sons Ltd. ISSN : 0556-3860 Library of Congress Catalog Card No. ![]() The Chemical Society Burlington House, London W I V OBN ![]() 1.Reid, Universify of Kent at Canferbury K. Bryce-Smith, Department of Chemistry, University of Reading Reporters M. A Review of the Literature Published between July 1974 and June 1975 ![]()
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