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= Molecular Chemistry and Spectroscopy - basic concepts =

Physical and chemical properties of molecules derive from their structures which in turn are defined by the chemical bonds tying atoms together. The nature of various chemical bonds is the domain of quantum chemistry which is de facto quantum physics applied to the particular problem structure of matter. In order to understand how and why atoms form molecules it is necessary to introduce some basic concepts of quantum chemistry. The aim of this book is to achieve it in a graphical way, based on the notion of symmetry and using as little mathematics as possible. In fact, the mathematical frame of this text does not go beyond the four basic mathematical operations and some odd roots and powers.

The most powerful and fundamental concept of quantum chemistry is wave function (ψ). It states that location and movement of small material objects on the atomic scale (measured in nanometers (nm)) is best achieved by associating with an object (say: an electron) a sinusoidal-like function. It is a striking assumption since position and trajectories of macroscopic objects we are used to describe by giving their Cartesian coordinates and their evolution in time.