STRUCTURE AND VIBRATIONAL FORCE-FIELD OF METHYLDIFLUOROAMINE, CH3NF2 - AN ELECTRON-DIFFRACTION INVESTIGATION AUGMENTED BY MICROWAVE AND INFRARED SPECTROSCOPIC DATA AND BY AB-INITIO MOLECULAR-ORBITAL CALCULATIONS

The structure of methyldifluoroamine, CH3NF2, was determined by gas-ph ase electron diffraction augmented by rotational constants from microw ave spectroscopy taken from the literature and by results from molecul ar orbital calculations. The structural results are consistent with C- s symmetry for a molecule with staggered bonds. The experimental bond distances and bond angles (r(alpha)(o)/r(g)) and angle(alpha)), with e stimated 2 sigma uncertainties are C-H = 1.104/1.124(5) Angstrom (aver age value), N-F = 1.406/1.408(2) Angstrom, C-N = 1.467/1.469(6) Angstr om, C-N-F = 104.1(2)degrees, F-N-F = 101.7(2)degrees, N-C-H-anti = 109 .9(11)degrees N-C-H-gauche = 106.5(10)degrees H-gauche -C-H-gauche = 1 10.6(28)degrees; the subscripts indicate orientation with respect to t he nitrogen lone pair. A scaled quantum-mechanical (SQM) quadratic vib rational force field was evaluated by symmetrizing the quantum-mechani cal (MP2/6-311++G(d,p)) Cartesian force constants and scaling the resu lts to fit observed infrared wavenumbers from the literature. The N-F; stretching force constants for the other fluoroamines NF3 and (CH3)(2 )NF were also determined in a similar fashion. Contrary to an earlier report, the values were found to increase with decreasing bond length consistent with Badger's rule.