Out-of-Plane CH2 Bending Potential Functions of Diazomethane, Ketene, and Related Molecules

Abstract

The unusually low out‐of‐plane CH₂ bending potential constants of ketene and diazomethane are discussed in terms of a valence bond comparison of their electronic structures to those of ethylene and ammonia. The anharmonic energy levels of the CH₂ out‐of‐plane bending in diazomethane are fitted with an harmonic‐quartic potential function. V(γ)=(½(2.74)·Δγ²+0.651·Δγ ⁴ × 10^—13 erg. A model is developed in which potential constants are transferred from the ethylene and ammonia molecules to the two valence‐bond structures usually considered for the ketene and diazomethane molecules. The unusually high intensities of the bending overtones are found to be a necessary consequence of this treatment. A further experimental test may be found in the expected large change in dipole moment with vibrational state. The model provides a basis for understanding the potential functions of ketene and diazomethane, and for making qualitative predictions about other molecules such as cyanamide and CF₂N₂.