Spectroscopy

Principles and Instrumentation

Mark F. Vitha

• Editore: Wiley
• Anno: 2018
• ISBN:
  9781119436607
• Edizione: 1
• Argomento: Physical Sciences
• Categoria: Spectroscopy & Spectrum Analysis

Provides students and practitioners with a comprehensive understanding of the theory of spectroscopy and the design and use of spectrophotometers

In this book, you will learn the fundamental principles underpinning molecular spectroscopy and the connections between those principles and the design of spectrophotometers.

Spectroscopy, along with chromatography, mass spectrometry, and electrochemistry, is an important and widely-used analytical technique. Applications of spectroscopy include air quality monitoring, compound identification, and the analysis of paintings and culturally important artifacts. This book introduces students to the fundamentals of molecular spectroscopy – including UV-visible, infrared, fluorescence, and Raman spectroscopy – in an approachable and comprehensive way. It goes beyond the basics of the subject and provides a detailed look at the interplay between theory and practice, making it ideal for courses in quantitative analysis, instrumental analysis, and biochemistry, as well as courses focused solely on spectroscopy. It is also a valuable resource for practitioners working in laboratories who regularly perform spectroscopic analyses.

Spectroscopy: Principles and Instrumentation:

• Provides extensive coverage of principles, instrumentation, and applications of molecular spectroscopy
• Facilitates a modular approach to teaching and learning about chemical instrumentation
• Helps students visualize the effects that electromagnetic radiation in different regions of the spectrum has on matter
• Connects the fundamental theory of the effects of electromagnetic radiation on matter to the design and use of spectrophotometers
• Features numerous figures and diagrams to facilitate learning
• Includes several worked examples and companion exercises throughout each chapter so that readers can check their understanding
• Offers numerous problems at the end of each chapter to allow readers to apply what they have learned
• Includes case studies that illustrate how spectroscopy is used in practice, including analyzing works of art, studying the kinetics of enzymatic reactions, detecting explosives, and determining the DNA sequence of the human genome
• Complements Chromatography: Principles and Instrumentation

The book is divided into five chapters that cover the Fundamentals of Spectroscopy, UV-visible Spectroscopy, Fluorescence/Luminescence Spectroscopy, Infrared Spectroscopy, and Raman Spectroscopy. Each chapter details the theory upon which the specific techniques are based, provides ways for readers to visualize the molecular-level effects of electromagnetic radiation on matter, describes the design and components of spectrophotometers, discusses applications of each type of spectroscopy, and includes case studies that illustrate specific applications of spectroscopy.

Each chapter is divided into multiple sections using headings and subheadings, making it easy for readers to work through the book and to find specific information relevant to their interests. Numerous figures, exercises, worked examples, and end-of-chapter problems reinforce important concepts and facilitate learning.

Spectroscopy: Principles and Instrumentation is an excellent text that prepares undergraduate students and practitioners to operate in modern laboratories.

1
FUNDAMENTALS OF SPECTROSCOPY

All instruments are designed to take advantage of some molecular property or behavior. For example, chromatography is based on the different strength of intermolecular interactions that molecules have with mobile and stationary phases. Electrochemistry is based on the ability of molecules to gain or lose electrons. In this book, we focus on the fact that atoms and molecules absorb and emit electromagnetic radiation (EMR). By measuring the amount and the characteristics of the EMR absorbed and emitted, we can measure the concentration of particular molecules present in a sample or gain structural information about them. You may already be familiar with several of the instrumental methods used to measure the absorption and emission of electromagnetic radiation, such as UV‐visible, infrared (IR), and fluorescence spectroscopy.

In order to better understand the fundamental basis of these techniques, in this chapter we examine the properties of electromagnetic radiation and its effects on atoms and molecules. In subsequent chapters, we examine specific spectroscopic techniques. While all the techniques share common features, the specific instruments required and the information we gain from each are quite different and therefore require individual examination.

1.1. PROPERTIES OF ELECTROMAGNETIC RADIATION

Spectroscopic methods ultimately rely on measuring characteristics of electromagnetic radiation, which travels through space as a wave, as shown in Figure 1.1. As the name implies, it has two components, an electric field and a magnetic field, which are at right angles to one another. Figure 1.1 shows only a single wave with its electric field oriented along the x‐axis, but in reality, most sources of electromagnetic radiation, like light bulbs and car headlights, emit radiation in which the electric field of the waves are randomly distributed around the x‐axis. For now, however, we take a simplified view by focusing on only a single electromagnetic wave.

FIGURE 1.1 Diagram of a single electromagnetic wave propagating through space. The diagram indicates that an electromagnetic wave has both an electric field (E) and magnetic field (B) associated with it and that they are oriented at right angles to each other. It also indicates that the wavelength (λ) is the distance the wave travels during one oscillation of the electric and magnetic fields.

Source: Reproduced with permission of Eric Clarke.

All electromagnetic waves have the properties of:

1. Speed
2. Amplitude
3. Frequency
4. Wavelength
5. Energy

Each of these characteristics is described below.

1.1.1. Speed, c

Electromagnetic radiation in a vacuum travels at 2.998 × 10⁸ m/s, commonly referred to as the speed of light, c. This speed only pertains to light traveling in a vacuum, though, because EMR slows down when it travels through matter such as air and water. We discuss the speed of light when it travels through matter in a later section.

1.1.2. Amplitude, A

The amplitude, A, of a wave is the maximum length of the electric field vector, as shown in Figure 1.2. We seldom consider the amplitude of the wave because detectors are not fast enough to measure the magnitude of the electric field vector. Instead, we measure the radiant power, P, of a beam, which is proportional to the square of the amplitude. Radiant power is the amount of energy transmitted per unit time and is given by Eq. (1.1), where E is the energy of a photon and φ is the flux (i.e., the number of photons per unit time) [1]:

(1.1)

FIGURE 1.2 A side view of the electric field component of an electromagnetic wave as it propagates from left to right across the page. The amplitude is the displacement along the y‐axis and the wavelength is the peak‐to‐peak distance between a single oscillation of the wave.

Although radiant power is commonly referred to as intensity, I, intensity is strictly defined as the radiant power from a point source per unit solid angle, usually measured in watts per steradian [1, 2].

1.1.3. Frequency, υ

Frequency, υ, is the number of oscillations a wave makes per unit time and is typically measured in hertz, Hz, with units of reciprocal seconds, 1/s or s⁻¹. To visualize the physical meaning of frequency, imagine sitting on a rock out in the ocean with a stopwatch and coun...