Abstract: A novel connectivity topological index( ^mB) based on the adjacency matrix and the ionic parameter of binding force(b_i) was derived in the present paper. The 0 and 1 order indexes⁰B and ¹B of ^mB were derived to correlate the long wavelength limit(λ) and the lattice energy (U) of 23 different types of transparent ionic crystals in infrared range. The relative coefficients (R=0.96904,
0.98523, 0.99185, 0.97635) of the derived equations are all in the range of higher level standards. Therefore, the results of present research could be useful for the design and evaluation of the long wavelength limit of ionic crystals.

Key words: long wavelength limit, binding force parameter, lattice energy, connectivity index