1. For a recent review of much of the relevant literature see M. P. Bogaard and B. J. Orr,International Review of Science. Physical Chemistry, edited by A. D. Buckingham (Butterworths, London, 1975), Ser. 2, Vol. 2, p. 149.
2. Perturbation theory of the non-linear optical polarization of an isolated system
3. J. W. Smith,Electric Dipole Moments(Butterworths, London, 1955).
4. A. I. Vogel et al. in a series of 52 papers published in J. Chem. Soc. between 1934 and 1966. The last paper in the series is J. Chem. Soc. B1966, 1080.
5. R. J. W. LeFèvre,Advances in Physical Organic Chemistry, edited by V. Gold (Academic, New York, 1965), Vol. 3, P. 1.