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Chapter 6:
Quantum Mechanics and Spectroscopy
To date, the physical theory that most accurately describes the behavior of the atomic world is quantum mechanics. Since spectroscopy uses light to probe the atomic and molecular world, it should not be much of a surprise to learn that quantum mechanics is used to describe how spectroscopy works. Nobel Prize-winning physicist Richard Feynmann once said, "€œIf you think you understand quantum mechanics, you don't understand quantum mechanics." This chapter won't bring you to a complete understanding of quantum mechanics, Feynmann's quote notwithstanding. But it will try to point out the important aspects, and hopefully it will at least leave the reader with the understanding that spectroscopy is quantum-mechanically based. Science's job is to try to understand the natural universe. To do this, scientists try to generate models to describe and predict the universe's behavior. (Not the behavior of the entire universe, but small selected parts of it.) If the model and the universe do not agree, there are two choices: change the model, or change the universe. Since all attempts at changing the universe have failed, our only choice is to change the model. Since the 1600s, scientific advance has accelerated at least in part because the proposed models of the universe have been increasingly more acceptable. Perhaps the first true “scientific” investigation (by the modern definition) was Robert Boyle's investigation of gases in the 1660s. While there were some noteworthy incorrect or improper models developed (phlogiston and vitalism are two that come to mind immediately, but doubtless there are others), incorrect or improper models were ultimately replaced by more viable models. One such group of models was what we now call Newton's laws of motion. In just a few statements, verbal or mathematical, Newton's laws accurately describe the motion of matter. Further, these models withstood the test of multiple examinations, and are accepted as proper models of how matter behaves.
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