Quantum Mechanical Foundations of Molecular Spectroscopy

Max Diem

• Publisher: Wiley-VCH
• Year: 2021
• ISBN:
  9783527829606
• Edition: 1
• Topic: Sciences physiques
• Subtopic: Spectroscopie et analyse du spectre

A concise textbook bridging quantum theory and spectroscopy!

Designed as a practical text, Quantum Mechanical Foundations of Molecular Spectroscopy covers the quantum mechanical fundamentals of molecular spectroscopy from the view of a professional spectroscopist, rather than a theoretician. Written by a noted expert on the topic, the book puts the emphasis on the relationship between spectroscopy and quantum mechanics, and provides the background information and derivations of the subjects needed to understand spectroscopy including: stationary energy states, transitions between these states, selection rules, and symmetry.

The phenomenal growth of all forms of spectroscopy over the past eight decades has contributed enormously to our understanding of molecular structure and properties. Today spectroscopy covers a broad field including the modern magnetic resonance techniques, non-linear, laser and fiber-based spectroscopy, surface and surface-enhanced spectroscopy, pico- and femtosecond time resolved spectroscopy, and many more. This up-to-date resource discusses several forms of spectroscopy that are used in many fields of science, such as fluorescence, surface spectroscopies, linear and non-linear Raman spectroscopy and spin spectroscopy. This important text:

• Contains the physics and mathematics needed to understand spectroscopy
• Explores spectroscopic methods the are widely used in chemistry, biophysics, biology, and materials science
• Offers a text written by an experienced lecturer and practitioner of spectroscopic methods
• Includes detailed explanations and worked examples

Written for chemistry, biochemistry, material sciences, and physics students, Quantum Mechanical Foundations of Molecular Spectroscopy provides an accessible text for understanding molecular spectroscopy.

1
Transition from Classical Physics to Quantum Mechanics

At the end of the nineteenth century, classical physics had progressed to such a level that many scientists thought all problems in physical science had been solved or were about to be solved. After all, classical Newtonian mechanics was able to predict the motions of celestial bodies, electromagnetism was described by Maxwell's equations (for a review of Maxwell's equations, see [1]), the formulation of the principles of thermodynamics had led to the understanding of the interconversion of heat and work and the limitations of this interconversion, and classical optics allowed the design and construction of scientific instruments such as the telescope and the microscope, both of which had advanced the understanding of the physical world around us.

In chemistry, an experimentally derived classification of elements had been achieved (the rudimentary periodic table), although the nature of atoms and molecules and the concept of the electron's involvement in chemical reactions had not been realized. The experiments by Rutherford demonstrated that the atom consisted of very small, positively charged, and heavy nuclei that identify each element and electrons orbiting the nuclei that provided the negative charge to produce electrically neutral atoms. At this point, the question naturally arose: Why don't the electrons fall into the nucleus, given the fact that opposite electric charges do attract? A planetary‐like situation where the electrons are held in orbits by centrifugal forces was not plausible because of the (radiative) energy loss an orbiting electron would experience. This dilemma was one of the causes for the development of quantum mechanics.

In addition, there were other experimental results that could not be explained by classical physics and needed the development of new theoretical concepts, for example, the inability of classical models to reproduce the blackbody emission curve, the photoelectric effect, and the observation of spectral “lines” in the emission (or absorption) spectra of atomic hydrogen. These experimental results dated back to the first decade of the twentieth century and caused a nearly explosive reaction by theoretical physicists in the 1920s that led to the formulation of quantum mechanics. The names of these physicists – Planck, Heisenberg, Einstein, Bohr, Born, de Broglie, Dirac, Pauli, Schrödinger, and others – have become indelibly linked to new theoretical models that revolutionized physics and chemistry.

This development of quantum theory occupied hundreds of publications and letters and thousands of pages of printed material and cannot be covered here in this book. Therefore, this book presents many of the difficult theoretical derivations as mere facts, without proof or even the underlying thought processes, since the aim of the discussion in the following chapters is the application of the quantum mechanical principles to molecular spectroscopy. Thus, these discussions should be construed as a guide to twenty‐first‐century students toward acceptance of quantum mechanical principles for their work that involves molecular spectroscopy.

Before the three cornerstone experiments that ushered in quantum mechanics – Planck's blackbody emission curve, the photoelectric effect, and the observation of spectral “lines” in the hydrogen atomic spectra – will be discussed, electromagnetic radiation, or light, will ...