HYPERFINE STRUCTURE AND CENTRIFUGAL DISTORTION IN MICROWAVE SPECTRA.

Abstract

The microwave spectra of CH₃I were measured on a C-band Stark cell microwave spectrometer. The lines were analyzed assuming that the quadrupole coupling eQq should be replaced by eQ(aJ(J + 1) + bK² + cK⁴/(J(J + 1)) + d) due to the presence of quadrupole centrifugal distortion. Explicit expressions were derived for a, b, and c in terms of molecular parameters. The values of a, b, and c were calculated for CH₃I and CD₃I and agree reasonably well with the experimental values. An algorithm was devised for the determination of the effect of hyperfine coupling on rotational energy levels in a molecule containing up to four nuclei of arbitrary spin. The uncoupled representation was used, and matrix elements were derived for spin-spin, spin-rotation, quadrupole, and Stark interactions. The case of three equivalent nuclei with spin of 1 was discussed. The microwave spectrum of phosphine-d₂ was measured and analyzed using two structural and three centrifugal distortion constants. Using molecular properties of phosphine, the centrifugal distortion tensor of phosphine-d₂ was calculated and the centrifugal distortion constants were determined. Only one of the three centrifugal distortion constants agreed well with the experimental value, suggesting that more data at higher frequencies is needed. The possibility of an electric hexadecapole interaction in CH₃I was discussed. A relationship between the magnitudes of the electric hexadecapole coupling constant and the d-orbital character of iodine in the C-I bond was derived. A gaussmeter specifically built for the determination of magnetic field in an Electron Paramagnetic Resonance experiment was described. A schematic diagram as well as a discussion of hardware was included.