G. Herzberg, Molekülspektren und Molekülstruktur. I. Zweiatomige Moleküle (Wissenschaftliche Forschungsberichte. Naturwissenschaftliche Reihe, B. 50), 404 pp., 169 ill., Leipzig, Steinkopff, 19391.

G. Herzberg, Molecular Spectra and Molecular Structure, Vol. I. Diatomic Molecules, 404 pp., 169 ill., Leipzig, Steinkopff, 1939.

Herzberg’s book is devoted to a systematic consideration of molecular spectra and their connection with the structure of molecules. The material included here is divided into two volumes: in the first volume the author deals with diatomic molecules, while in the second volume, not yet published, the spectra of polyatomic molecules will be discussed.

Molecular spectra are a most important source of information on the structure of molecules. At the same time, the study of molecular spectra makes it possible to judge elementary processes in gases (in particular, in the atmospheres of celestial bodies), intermolecular forces, and certain properties of atomic nuclei (spin and statistics), etc.

For this reason molecular spectra have to be studied by a wide circle of people—physicists, chemists, and astrophysicists. Taking this circumstance into account, the author has tried, and has succeeded, in making the book as accessible as possible and not overburdening it with complicated mathematical methods, usually unfamiliar to chemists.

In a brief introduction, in addition to several general remarks, the values of atomic constants are given and the connection between various energy units is indicated \((\mathrm{cm}^{-1}, \mathrm{kcal}/\mathrm{mol},\) etc.).

Chapter I briefly sets out the foundations of the theory of the atom and atomic spectra. This chapter has no independent significance and is intended only to establish the connection between the theory of atomic spectra and the subsequent exposition. A more detailed introductory chapter was unnecessary for the author, since he had the possibility of referring to his earlier book Atomspektren und Atomstruktur.

In Chapter II the author proceeds to a description of the observed spectra of diatomic molecules and to the establishment of certain simplest empirical regularities to which they are subject. The clarity of the exposition here is greatly helped by the presence of a large number of clear photographs of emission and absorption spectra of various molecules, as well as spectra of combination scattering. This chapter is not overloaded with extensive empirical material and contains only the principal experimental data necessary for what follows.

In Chapter III the rotation and vibration of diatomic molecules and their connection with the theory of infrared and combination (Raman) spectra are considered. Here the author, as throughout the book, makes fairly extensive use of the results of quantum-mechanical calculations. The author does not present the calculations, but the initial equations are usually indicated; the results obtained after solving them are illustrated (for example, graphs of the wave functions \(\Psi\) and probabilities \((\Psi)^2\) are given). The exposition is conducted (this is also characteristic of the whole book) by proceeding from simple

cases to more complex ones. For example, molecular models are analyzed in the following sequence: rigid rotator, oscillator, anharmonic oscillator, oscillating rotator, symmetric top. The applicability of each model is illustrated by a large number of examples. In this same chapter (III) questions concerning the intensity of infrared spectra, the influence on these spectra of the spin of the nucleus, the symmetry of terms, etc., are discussed.

In the next two chapters (IV–V), the electronic states and electronic transitions of diatomic molecules are studied in detail. The enormous material is presented clearly, but nevertheless undoubtedly requires considerable diligence for its assimilation. A detailed and complete exposition of a number of difficult questions (for example, the relation of the molecule’s rotation to the motion of electrons and the general systematics of electronic-vibrational-rotational transitions) gives the book undoubted scientific interest.

Questions of molecular structure in connection with the theory of its spectra are treated in Chapter VI. The exposition here is predominantly qualitative in character. Even in describing the theory of the hydrogen molecule, the author does not use quantum mechanics and confines himself only to remarks of a descriptive nature.

Chapter VII considers continuous molecular spectra, as well as the dissociation and predissociation of molecules.

In the last, VIII, chapter a survey is given of the results of investigations of diatomic molecules, and various examples are also given and applications of molecular spectroscopy in physics, chemistry, and astrophysics are discussed.

A fairly rich bibliography, brought up to the middle of 1938, as well as detailed name and subject indexes, facilitate the use of the book for reference.

The systematic character and individual method of exposition make it possible to use the book for an initial acquaintance with molecular spectra; the variety of material discussed and the detailed treatment of a number of difficult questions at the same time make it valuable for the specialist.

We have noticed no significant inaccuracies in the book. However, one may point out certain deficiencies, perhaps generally unavoidable in a book. The author considers a broad range of questions connected with molecular spectra and the structure of molecules. Therefore the complete absence of even the briefest description of methods of obtaining and investigating these spectra is difficult to understand. One may also regret that the author did not include in the book, as material necessary for reading it, an exposition of the quantum-mechanical theory of molecular spectra and of the molecular bond. In specialized works these questions are treated, but usually in a general form that is not very accessible. Including them even in the simplest form would have given the book greater completeness.

The remarks made, of course, cannot diminish the scientific and pedagogical merits of Herzberg’s book. It is written clearly and systematically and represents a valuable contribution to world scientific literature. A translation of the book into Russian is desirable.

V. Ginzburg, Moscow

1. Based on materials of the Information-Bibliographic Sector of the State Scientific Library of the People’s Commissariat of Coal of the USSR. ↩