Introduction

This book is about the interaction of light with matter. Nearly all of the phenomena that are produced by means of this interaction can be called spectroscopic, in the broadest sense of the term. Included are the ordinary processes of absorption and emission of radio waves, microwaves, and infrared, visible, and ultraviolet light, which leave the associated atoms, ions, or molecules chemically intact. Such phenomena are used by synthetic and analytic chemists in the identification and characterization of substances, and by physical chemists in elucidating molecular structure, determining bond strengths, and studying relaxation processes. When light in the optical region of the spectrum is employed, such effects provide the microscopic basis for theories of color and vision. The explanation of absorption and emission is the purpose of subsequent chapters.