Microwave spectrum of dibromomethane. Part 2.—Nuclear quadrupole coupling tensor

Abstract

The nuclear quadrupole hyperfine structure in the spectra of four isotopic species of dibromomethane, CH279Br2,CH281Br2,CD279Br2 and CD281Br2, has been analyzed to give the quadrupole coupling tensor directly, using second-order perturbation theory. Coupling constants (MHz) in the principal inertial axes system are as follows, CH279Br2: χaa= 334.9 ± 12, χbb=–25.2 ∓ 6, χcc=–309.7 ∓ 6, χab= 395.9 ± 13; CH281Br2: χaa= 280.6 ± 6, χbb=–21.4 ∓3, χcc=–259.2 ∓ 3, χab= 332.5 ± 10. Consistent values are reported for CD279Br2 and CD281Br2. Diagonalization of the quadrupole coupling tensor yields, CH279Br2: χzz= 591 ± 20, χxx=–281∓14, χyy=–310 ∓ 6 and CH281Br2: χzz= 495 ± 12, χxx=–236∓9, χyy=–259.2∓3. It is concluded that the Br-bond projection coincides with the internuclear axis within the experimental error of 1°; if bent bonding is involved in the C—Br bond the bend cannot be more than the experimental error of 2°. The analysis of the nuclear quadrupole hyperfine structure of a dibromine molecule is outlined and a comprehensive list of assignments presented in an appendix.