1. (a) Shaik SS, Schlegel HB, Wolfe S (1992) Theoretical aspects of physical organic chemistry: the SN2 Mechanism. Wiley, New York. See particularly Introduction and chapters 1 and 2.
2. (b) Marcus RA (1992) Science 256, 1523
3. (c) For a very abstract and mathematical but interesting treatment, see Mezey PG (1987) Potential energy hypersurfaces. Elsevier, New York
4. (d) Steinfeld JI, Francisco JS, Hase WL (1999) Chemical kinetics and dynamics, 2d ed. Prentice Hall, Upper Saddle River
5. Levine IN (2014) Quantum chemistry, 7th edn. Prentice Hall, Upper Saddle River, NJ, section 4.3