Electron Distribution in the C–Cl Bonds of CH2Cl2 and Derivation of Matrix Elements Off-Diagonal in J for Two Quadrupolar Nuclei in an Asymmetric Rotor

The microwave spectrum of methylene chloride has been reinvestigated with the high‐resolution spectrometer now available. The diagonal quadrupole coupling constants of Cl in CH₂Cl₂³⁵ were remeasured under high resolution, giving χ_aa=—41.07±0.01 Mc, χ_bb=1.24±0.02 Mc, and χ_cc=+39.83±0.01 Mc. By using second‐order perturbation theory, the off‐diagonal element χ_ab was measured directly and was —52±3 Mc. These results show that the C–Cl bond in methylene chloride is not bent within an experimental error of 1°. Matrix elements off‐diagonal in J, of the quadrupole interaction Hamiltonian for two quadrupolar nuclei, are derived using Racah coefficients. The $I_1{\mathrm{=I}}_2=\frac{3}{2}$ matrix elements are evaluated and listed in the Appendix.