Microwave Spectrum, Structure, and Nuclear Quadrupole Coupling Constant Tensor of Iodomethyl Methyl Ether

Microwave spectra of iodomethyl methyl ether and its 10 isotopic species have been measured. A least-squares analysis of the observed frequencies gave rotational and quartic centrifugal distortion constants and all the components of the nuclear quadrupole coupling constant tensor. The rsstructure has been well established from the moments of inertia calculated from the observed rotational constants. The observed nuclear quadrupole coupling constant tensor in the inertial principal axes system could be transformed into that in its own principal axes system. The directions of the χ principal axes in the molecule were found to be closely related to the signs of three off-diagonal χ components in the inertial principal axes system which could not be determined by the least-squares fit of the observed frequencies. The signs of the three off-diagonal χ components were concluded to be (+, +, −) for χab, χac, and χbc, respectively. The zaxis of the principal χ system is roughly along the CI bond, while the xaxis is no longer in the OCI plane but is inclined by about 6°30′ toward the side where the CH3group exists. The molecular structure and nuclear quadrupole coupling constant tensor of the present molecule were compared with those of the other halomethyl ethers, alkyl halides, and alkyl ethers.