Bibliography

A. G. MITCHELL and M. W. ZEMANSKY, Resonance Radiation and Excited Atoms. Cambridge University Press (The Cambridge Series of Physical Chemistry, Edited by E. K. Rideal), 1934, pp. XVI + 338 *

MITCHELL and ZEMANSKY, Resonance Radiation and Excited Atoms.

The study of resonance radiation is one of the most interesting and important problems of modern physics. The appearance, therefore, of the book under review in E. K. Rideal’s series of physicochemical monographs is exceptionally timely. This publication is especially to be welcomed because, despite the thirty-year history of the subject, it has hitherto been impossible to point to a single book that would give a complete picture of the state of the entire field.

Let us turn to a survey of the contents of the book. Chapter I is introductory in character; it gives general information on spectra, provides a qualitative description of the phenomenon of resonance fluorescence, and presents the necessary data concerning experimental technique (light sources, resonance lamps).

Chapter II considers the physical and chemical phenomena connected with resonance radiation. Among the former are stepwise excitation (the experiments of Fochtbauer and Wood), the influence of foreign gases, the appearance of forbidden lines in the presence of impurities, and sensitized fluorescence; among the latter are sensitized photochemical processes.

Chapters III and IV (pp. 92–258), in scope and importance, constitute the main content of the book. Chapter III is devoted to absorption lines and to the problem of determining the lifetime of excited states. The chapter opens with an exposition of Einstein’s theory of radiation, introduces the Einstein transition probabilities, establishes the concept of oscillator strengths in the language of the classical dispersion theory, and sets forth their quantum interpretation. There follows a very detailed analysis of the structure and properties of absorption lines: absorption at the edges and within lines, magnetic rotation, and anomalous dispersion at the edges of lines. Finally, direct methods for determining the lifetimes of excited states are described (measurement of attenuation in a molecular beam, the Hanle method, Bina’s channel-beam method), and the results obtained by the various methods are compared.

Chapter IV examines the collision processes of excited atoms. Here, first of all, the question of the broadening of spectral lines is discussed in great detail, with the greatest attention naturally being devoted to the so-called “Lorentz broadening,” i.e. broadening due to collisions with atoms of a foreign gas, and to “Holtsmark broadening,” caused by collisions with atoms of the absorbing gas itself. The remaining part of the chapter is devoted to the quenching of fluorescence by foreign gases, to exceedingly interesting questions of the so-called “diffusion” of resonance radiation, i.e. the “wandering” of resonance radiation within

* Based on materials of the Critical-Bibliographical Scientific Research Institute.

gas as a result of its capture by ever new atoms—a phenomenon first discovered by one of the authors of the book, M. Zemansky; and, finally, to collisions of excited atoms obtained by optical dissociation.

Chapter V, the last, is devoted to the polarization of resonance radiation and to various effects on the state of polarization: magnetic depolarization, depolarization as a result of collisions.

Each chapter ends with a systematic index of the original literature.

As is clear from the above survey of the contents, the book gives a very complete picture of the present state of the question. A great merit of the book is the remarkable clarity of exposition. The physical aspect of the problems considered is everywhere set forth with perfect distinctness and is nowhere obscured by long mathematical derivations. It is true that in many cases the authors do not give the derivations at all and confine themselves to presenting the final formulae, but the most important derivations are given in the text and especially in the special mathematical appendices. In going through the book, the Soviet reader will note with great satisfaction that, in the investigation of these questions—so interesting and so delicate both theoretically and experimentally—the work of our Soviet scholars plays a very considerable role. The works of Rozhdestvensky, Prokofiev, Filippov, Terenin, Kondrat’ev, Landau, and others constitute a significant contribution to this extensive and interesting field of physics.

E. Shpol’skii