1. Uma Kapoor and Nigam, H. L.D.Phil. Thesis, University of Allahabad, 1961.
2. Nigam, H. L., Kapoor, R. C., Uma Kapoor and Srivastava, S. C.Indian J. Chem., 1965,3(12), 527.
3. Mande, C. and Chetal, A. R.Proc. Ind. Acad Sci., 1965,62 A (2), 97.
4. Mathur, V. K. and Nigam, H.L.Naturwissenschaften, 1964,51 (2), 35.
5. Pauling, L. ..Nature of Chemical Bond, Oxford and IBH Publishing Co., 1963, pp. 165–66.