Abstract

The ir spectra from 4000 to 33 cm⁻¹ have been recorded of CH₃AsCl₂, CH₃AsBr₂, CH₃AsI₂, and CD₃AsI₂. The Raman spectra of each of these compounds have been recorded and depolarization values measured for CH₃AsCl₂ and CH₃AsBr₂. The observed spectra have been successfully interpreted on the basis of a pyramidal skeletal structure of C_s symmetry. The observed values for the Teller-Redlich product rule for the assignments of the normal modes of the CH₃AsI₂ and CD₃AsI₂ molecules are in reasonable agreement with the theoretical values for both symmetry species. The As–CH₃ torsional mode was tentatively assigned in the ir spectrum of solid CH₃AsBr₂ at 134 cm⁻¹ and the torsional barrier calculated to be 461±30 cm⁻¹ (1.32±0.08 kcal/mole). The low frequency bending modes of solid CH₃AsI₂ and CD₃AsI₂ have been found to show correlation field splitting and have been successfully explained in terms of the four molecules per unit cell with a space group of <i>C_2h⁶</i>.

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