The Quantum Mechanics of Atoms and Molecules

Walter E Thirring, Evans M. Harrell

A. F. J. Levi

Motivation You may ask why one needs to know about quantum mechanics. Possibly the simplest answer is that we live in a quantum world! Engineers would like to make and control electronic, opto-electronic, and optical devices on an atomic scale. In biology there are molecules and cells we wish to understand and modify on an atomic scale. The same is true in chemistry, where an important goal is the synthesis of both organic and inorganic compounds with precise atomic composition and structure. Quantum mechanics gives the engineer, the biologist, and the chemist the tools with which to study and control objects on an atomic scale. As an example, consider the deoxyribonucleic acid (DNA) molecule shown in Fig. 1.1. The number of atoms in DNA can be so great that it is impossible to track the position and activity of every atom. However, suppose we wish to know the effect a particular site (or neighborhood of an atom) in a single molecule has on a chemical reaction. Making use of quantum mechanics, engineers, biologists, and chemists can work together to solve this problem. In one approach, laser-induced fluorescence of a fluorophore attached to a specific site of a large molecule can be used to study the dynamics of that individual molecule. The light emitted from the fluorophore acts as a small beacon that provides information about the state of the molecule.

Narciso N. Garcia, Arthur C. Damask, Steven A. Schwarz

Don DeVault

‘Tunnelling’ is the metaphorical name given to the process, possible in quantum mechanics, but not in classical mechanics, whereby a particle can disappear from one side of a potential-energy barrier and appear on the other side without having enough kinetic energy to mount the barrier. One can think of this as a manifestation of the wave-nature of particles. The wavelength is larger if a particle is lighter. In particular electrons, being very light compared to atoms, have wavelengths as large or larger than atoms at energies found in the valence shells of molecules. Thus, they easily ooze through and around atoms and molecules. We are also concerned with the tunnelling of heavy particles: nuclei, atoms, molecules.

Narciso N. Garcia, Arthur C. Damask

Robert M. Granger, Hank M. Yochum, Jill Nelson Granger +1 more

This chapter reviews the basic quantum mechanics of spectroscopy, analyzing forms of spectroscopy based on the measurement of energy as an atom or molecule undergoes a change in quantum states. It looks at different aspects of quantum mechanics in order to understand instrumental techniques and analysis involving the interaction of light and matter. It also looks at how spectroscopy explores particular energy level differences between quantum states in molecules and atoms. The chapter stresses the importance of quantum mechanics in the development of spectroscopic techniques used to investigate atomic composition and chemical structures. It cites an example that outlines the quantum mechanic events that led to the line spectrum of hydrogen in a gas in a discharge tube.