Internuclear distances in methylmercury chloride bromide and iodide from microwave spectra

Abstract

Rotational constants are reported for 31 previously unmeasured isotopic species of methylmercury chloride, bromide and iodide. The constants for CH₃HgI do not substantiate earlier measurements, and a new set of internally consistent constants for 15 isotopic species of methylmercury iodide is presented. Assignment of the spectra of the bromide and iodide is facilitated by the smallness of the effects of excitation of the bending mode, ν_s on the rotational constant.

Substitution lengths for the C—Hg bonds in these substances are derived for the first time. The accuracy of the Hg placement is insufficient for complete methyl group structures to be derived from the constants for CD₃ species, but a range of acceptable methyl group structures can be defined for the chloride and bromide, and an accurate Hg—I distance in methyl mercury iodide can be derived from first moment considerations. These structures are compared with those derived by least squares fitting procedures using arrays of rotational constants.