A NEW APPROACH TO THE NONPARAMETRIC DETERMINATION OF INTERNAL-ROTATION POTENTIAL FROM ELECTRON-DIFFRACTION DATA AS APPLIED TO REINVESTIGATION OF THE MOLECULAR-STRUCTURE OF M-BROMONITROBENZENE

A nonparametric numerical algorithm is suggested for calculation of th e torsional potential from gas electron diffraction data using Tikhono v's method of regularization. A new approach to determine the admissib le interval of the regularization parameter using Hamilton's statistic al test has been considered. Applied to this reinvestigation of m-brom onitrobenzene it was confirmed that this algorithm only allows the det ermination of the form of the torsional potential function near its mi nimum. The barrier to internal rotation was estimated to be 4.6-5.4 kc al mol(-1) as interpolated by Fourier series with proper parameterizat ion. The most important structural parameters (r(a) in Angstroms, angl e alpha in degrees) are: r(C-C)(av) = 1.399(3), r(C-N) = 1.459(16), r( N=O) = 1.244(3), r(C-Br)= 1.884(6), r(C-H) = 1.099(20), angle CCNC = 1 23.9(1.4), angle CNCCBr = 116.8(1.5), angle CNCC = 116.6(1.9), angle C NO = 118.8(0.8). The structure parameters are compared with those obta ined previously for o-, m-, and p-bromonitrobenzenes.