Which books do you recommend to learn more about the experiments that led to formulation of quantum theories? I am trying to understand the evolution of quantum mechanics, mainly the experiments that led to the formulation of quantum mechanics theories.
 A: I recommend

Max Jammer, The conceptual development of quantum mechanics, McGraw-Hill; 1966.

The book is somewhat old but many of the pioneers of quantum mechanics were still alive or had just recently passed away at the time of the writing, so that Jammer had access to primary sources, sometimes even interviewing key figures.
Of course it does suffer from its age in the sense that none of the exciting developments since then are mentioned, but nevertheless from a more historical perspective it remains a key reference precisely because it discusses lesser known aspects in the evolution of quantum theory.
The book is better understood if you have some knowledge of quantum mechanics, preferably at the undergraduate level.  Alternatively, if you are an undergraduate interested in a broader picture of the context, this book is at your level.
The book does cover the experimental basis of quantum mechanics, although the material is presented historically so that experimental and theoretical advances are intertwined in the presentation.
