Microwave Spectrum, Structure, and Quadrupole Coupling Constant Tensor of Ethyl Bromide

Abstract

The microwave spectra of 10 isotopic species of ethyl bromide have been measured and assigned, viz., the ⁷⁹Br and ⁸¹Br species of CH₃CH₂Br, CH₃CD₂Br, CD₃CH₂Br, CH₃¹³CH₂Br, and ¹³CH₃CH₂Br. The spectra reported lie in the region of 18 to 31 kMc. The complete structure has been determined by the substitution method, giving the following bond parameters: CC = 1.518 Å, CBr = 1.950 Å, CCBr = 111°2′, CH (methylene) = 1.087 Å, HCH (methylene) = 109°54′, CCH (methylene) = 112°15′, HCBr = 105°25′, CH (methyl) = 1.093 Å, and HCH (methyl) = 108°52′. The principal quadrupole coupling parameters have been determined to be χ_zz = 541 Mc, χ_xx = —267 Mc, and χ_yy = —274 Mc for C₂H₅⁷⁹Br and χ_zz = 450 Mc, χ_xx = —220 Mc, and χ_yy = —230 Mc for C₂H₅⁸¹Br. Through the analysis of second‐order effects of quadrupole coupling on hyperfine structure, it was determined that, within experimental error, the CBr internuclear line and the ``z'' principal quadrupole axis coincide, indicating that the CBr bond is not bent. The barrier to internal rotation, recalculated using Lide's splitting measurements, and the above structure is 3684 cal/mole.