K. F. BONHOEFFER und P. HARTECK, Grundlagen der Photochemie
(Die Chemische Reaktion, Herausgegeben von H. Mark und M. Polanyi, Band I),
Verlag von Theodor Steinkopff, Dresden und Leipzig 1933, Pp. VIII+295.

BONHOEFFER and HARTECK, Fundamentals of Photochemistry.

The first volume of the new series of monographs “Chemical Reaction,” published under the editorship of H. Mark and M. Polanyi, is devoted to photochemistry. Recent years have been marked by major successes in the study of molecular spectra. These successes could not fail to affect photochemistry and, thanks to Franck’s extraordinarily fruitful idea, in many cases made it possible to predict the course of primary processes with complete definiteness. The authors of the book under review therefore quite rightly assert that, at the time the book appeared, the principles of photochemistry could be regarded as having been finally clarified, and that a broad field of activity had opened up for their application.

However, an essential, though purely external, difficulty in this field is that until the very recent past the initiative in research belonged chiefly to physicists.

was almost exclusively in the hands of physicists. The unfamiliar and difficult experimental methodology, the need for extensive knowledge in the fields of spectroscopy, atomic physics, quantum mechanics—for the theoretical interpretation of results—all this prevented chemists from engaging in photochemistry. Added to this was the fact that until very recently there was not a single monograph in the literature that set forth everything necessary for understanding contemporary photochemical work, and moreover in a form accessible to chemists.

The authors set themselves the task of writing precisely such a book on photochemistry. It should be noted at the outset that they have accomplished this exceedingly difficult task very well, and therefore the appearance of Bonhoeffer and Harteck’s book must be recognized as a major achievement in the field of photochemistry.

In accordance with their principal aim—to lead the chemist reader toward an understanding of contemporary photochemical work—the authors devote two thirds of their book (180 pages out of 280) to purely physical questions, namely absorption spectra and their application to the interpretation of primary photochemical processes. Photochemical kinetics and the consideration of individual reactions occupy a smaller part of the book; moreover, only the most characteristic and best-investigated reactions have been selected, in order to show, by means of these examples, how, through a combination of purely physical data and kinetic analysis, one can arrive at an interpretation of the most delicate features of the reaction mechanism. Experimental methodology is not touched upon at all, for lack of space.

The book is divided into four parts. The first examines the photochemical law of equivalence. The essence of this fundamental law of photochemistry, which in its time gave rise to fierce polemics and numerous misunderstandings, has now become so clear, and the law itself so simple, that the authors quite rightly devote little space to it (10 pages), occupied mainly by tables of quantum yields. The second part is the central part of the book, both in volume (172 pages) and in significance. This part is devoted to the primary photochemical process and contains the foundations of the theory of molecular spectra (section A) and the application of this theory to the analysis of the primary process (section B). Section A is, of necessity, presented very briefly. For readers wishing to continue independent work in the field of photochemistry, reading this page of the book by Bonhoeffer and Harteck should serve as an incentive to study more extensive books on spectroscopy. Section B—“Absorption of Light and the Primary Process in Individual Photochemically Important Substances”—is of exceptional interest. The authors have collected extensive material with great competence and irreproachable conscientiousness, so that this section can serve not only for reading but also for constant reference.

The last two parts of the book (III and IV) are devoted to photochemical kinetics and the analysis of individual complex reactions. The character of these parts has been described above. The distinctive distribution of material in these parts deserves mention. The authors, in contrast to the usual division of photochemical reactions according to the magnitude of the quantum yield, classify secondary processes according to the character of the primary process and consider separately the properties of excited molecules and the properties of free atoms. Thus there is no need for a special chapter on photochemical sensitization.

The exposition is distinguished by great clarity. It is especially gratifying that the book provides a complete picture of the entire discipline and is not a collection of abstracts of individual works. One feels that the book has come from the hands of scholars who possess extensive personal experience and original points of view concerning the subject presented.

A Russian translation of Bonhoeffer and Harteck’s book is urgently needed.

E. Shpolsky