The structure of nitrogen gas

Abstract

The structure factor for nitrogen gas was measured between 0·3 < Q < 4 Å^-1 and at densities of 0·48 and 0·35 × 10²² molecules cm^-3 and temperatures of 296 and 200 K. We have tried to improve the methods used in this field so as to obtain data which are correct to ± 3 per cent in absolute scale and ± 1 per cent in shape. The data at room temperature are in agreement with the isothermal compressibility as Q → 0, but between 2 and 4 Å^-1 they fall below the single molecule structure factor by about 9 per cent. Also these measurements are compared with the results from the RISM theory by Johnson and Hazoumé [1] using models for the nitrogen potential published by Barojas, Levesque and Quentrec [2] and Cheung and Powles [3], who fitted their parameters to liquid nitrogen data. It is found that for 2 < Q < 4 Å^-1 the data are significantly below the predictions. Although the RISM theory is not exact, it is concluded that some of the discrepancy is fundamental. However, other (smaller) discrepancies may be due to the choice of parameters, the limitations of these potential models, or the failure of RISM, and further work is required to separate these possibilities.