Introduction to Experimental Infrared Spectroscopy

Fundamentals and Practical Methods

Mitsuo Tasumi, Mitsuo Tasumi

• Publisher: Wiley
• Year: 2014
• ISBN:
  9781118703540
• Edition: 1
• Topic: Ciencias físicas
• Subtopic: Espectroscopia y análisis de espectro

Infrared spectroscopy is generally understood to mean the science of spectra relating to infrared radiation, namely electromagnetic waves, in the wavelength region occurring intermediately between visible light and microwaves. Measurements of infrared spectra have been providing useful information, for a variety of scientific research and industrial studies, for over half a century; this is set to continue in the foreseeable future.

Introduction to Experimental Infrared Spectroscopy is intended to be a handy guide for those who have no, or limited, experience in infrared spectroscopic measurements but are utilising infrared-related methods for their research or in practical applications.

Written by leading researchers and experienced practitioners, this work consists of 22 chapters and presents the basic theory, methodology and practical measurement methods, including ATR, photoacoustic, IR imaging, NIR, 2D-COS, and VCD. The six Appendices will aid readers in understanding the concepts presented in the main text.

Written in an easy-to-understand way this book is suitable for students, researchers and technicians working with infrared spectroscopy and related methods.

Part I
Fundamentals of Infrared Spectroscopic Measurements

Chapter 1
Introduction to Infrared Spectroscopy

Mitsuo Tasumi

Professor Emeritus, The University of Tokyo, Japan

1.1 Introduction

Infrared spectroscopy is a useful tool for molecular structural studies, identification, and quantitative analyses of materials. The advantage of this technique lies in its wide applicability to various problems in both the condensed phase and gaseous state. As described in the later chapters of this book, infrared spectroscopy is used in chemical, environmental, life, materials, pharmaceutical, and surface sciences, as well as in many technological applications. The purpose of this book is to provide readers with a practical guide to the experimental aspects of this versatile method.

In this chapter, introductory explanations are given on an infrared absorption spectrum and related basic subjects, which readers should understand before reading the later chapters, on the assumption that the readers have no preliminary knowledge of infrared spectroscopy.

As is well known, visible light is absorbed by various materials and the absorption of visible light is associated with the colors of materials. Blue materials absorb radiation with a red color, and red materials absorb radiation with a blue color. The wavelengths of radiation with a red color are longer than those with a blue color. A diagram showing quantitatively the absorption of visible light at different wavelengths from violet to red is called a visible absorption spectrum. The visible absorption spectrum closely reflects the color of the material from which the spectrum is measured.

The wavelengths of infrared radiation are longer than those of radiation with red color. Radiation with red color has the longest wavelengths among visible light, the wavelength of which increases from violet to red. Infrared radiation, though not detectable by human eyes, is absorbed by almost all materials. An infrared spectrum is a plot quantitatively showing the absorption of infrared radiation against the wavelength of infrared radiation. It is usually possible to observe an infrared absorption spectrum from any material except metals, regardless of whether the sample is in the gaseous, liquid, or solid state. This advantage makes infrared spectroscopy a most useful tool, utilized for many purposes in various fields.

Measurements of infrared spectra are mostly done for liquid and solid samples. In the visible absorption spectra of liquids and solids, only one or two broad bands are typically observed but infrared absorption spectra show at least several, often many relatively sharp absorption bands. Most organic compounds have a significant number of infrared absorption bands. This difference between the visible and infrared absorption spectra is due to the different origins for the two kinds of spectra. Visible absorption is associated with the states of electrons in a molecule. By contrast, infrared absorptions arise from the vibrational states of atoms in a molecule. In other words, the visible absorption spectrum is an electronic spectrum and the infrared spectrum is a vibrational spectrum. Vibrational motio...