Microwave spectrum of dibromomethane. Part 1.—Molecular structure

Abstract

The microwave spectra of four isotopic species of dibromomethane, CH₂⁷⁹Br₂, CH₂⁸¹Br₂CD₂⁷⁹Br₂ and CD₂⁸¹Br₂, have been assigned and rotational constants derived in each case. Two possible molecular structures are discussed: (I)r_CBr= 1.930 ± 0.003 Å, r_CH= 1.079 ± 0.01 Å, ∠BrCBr = 112.5 ± 0.3°, ∠HCH = 113.6 ± 1.5° and (II)r_CBr= 1.925 ± 0.002 Å, ∠BrCBr = 112.9 ± 0.2°, ∠HCH = 110.9 ± 0.8° if r_CH is assumed to be 1.097 ± 0.005 Å. The Br…Br distance is accurately determined to be 3.2090 ± 0.0006 Å. The most probable values for the C—Br bond distance and ∠BrCBr are r_CBr= 1.927 ± 0.006 Å, ∠BrCBr = 112.7 ± 0.5°. For dibromomethane, as for dichloromethane, both ∠HCH and ∠XCX are larger than the regular tetrahedral angle of 109.5°. The structure is discussed in relation to the structure of other halogen substituted methanes.