Electron-Diffraction Study of Ammonia and Deuteroammonia

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Abstract
The gas‐phase structures of NH3 and ND3 molecules were determined by the sector‐microphotometer method of electron diffraction. The following internuclear distances rg and mean amplitudes le with estimated standard errors were obtained: For NH3, rg(N − H) = 1.0302 ± 0.002 Å, rg(H − H) = 1.662 ± 0.010 Å, le(N − H) = 0.0731 ± 0.002 Å, le(H − H) = 0.125 ± 0.006 Å , and for ND3, rg(N − D) = 1.0266 ± 0.003 Å, rg(D − D) = 1.654 ± 0.008 Å, le(N − D) = 0.0611 ± 0.002 Å, le(D − D) = 0.101 ± 0.006 Å , with the parameter κ representing bond‐stretching anharmonicity fixed at 1.0 × 10−5 and 0.5 × 10−5 Å3 for N–H and N–D, respectively. Effects of anharmonicity and isotope differences in the structural parameters analogous to those in CH4 and CD4 were observed. The rα0 and re bond distances calculated from the above rg distances are found to be consistent with the corresponding rz and re distances derived from the spectroscopic rotational constants of Benedict and Plyler. The isotope effects reported by Bell and by Halevi for the dipole moment and polarizability of ammonia are discussed briefly in the light of the present results.