Microwave spectrum and molecular structure of methylenimine (CH2NH)

Abstract

The microwave spectra of five new isotopic species of CH₂NH have been measured in the pyrolysis products of aqueous solutions of methylamine and 1,2‐diaminoethane. Rotational constants and moments of inertia have been determined for ¹³CH₂ ¹⁴NH, ¹²CH₂ ¹⁵NH, ¹²CH₂ ¹⁴ND, ¹²CD₂ ¹⁴NH, and ¹²CD₂ ¹⁴ND. These data have been combined with previous measurements of ¹²CH₂ ¹⁴NH to give r_s‐coordinates for the C, N, and imine‐H atoms, and the following structural parameters: r (CN) =1.273 Å, r (NH) =1.023 Å, and & HNC=110.5°. Methods for obtaining a complete structure, and uncertainties arising from the proximity of the C and N atoms to the principal a‐axis are discussed. A pseudo‐Kraitchman calculation constraining the CH distances to be equal gives the following (planar) structure: r (CN) =1.273 Å, r (NH) =1.021 Å, r (CH) =1.09 Å, & HNC=110.4°, & HCH=117.0°, and & NCH_cis =125.1°.