19F Spin—Rotation and Spin—Spin Interactions, 19F Magnetic Shielding, and Molecular Magnetic Moments for OCF2

Abstract

The microwave spectrum of OCF₂ is examined under high resolution using an L‐band waveguide and 1 and 5‐kc/sec modulation, where half‐widths at half‐height of 5–7 kc/sec are obtained. The ¹⁹F nuclear‐spin‐nuclear‐spin and the ¹⁹F spin—rotation interactions are observed. The experimental ¹⁹F spin—rotation constants along the principal inertial axes are M_aa = | 19±3 | kc/sec, M_bb = | 13±3 | kc/sec, and M_cc = | 5±3 | kc/sec. The calculated magnitude of the nuclear contribution to the ¹⁹F spin—rotation constants show that the signs of the above values are all negative, which then leads to the calculated ¹⁹F paramagnetic shielding in OCF₂ of σ^p = −324×10⁻⁶. The ¹⁹F chemical shift in OCF₂ is measured relative to Cl₃CF giving 23×10⁻⁶. Relating the ¹⁹F shielding back to F₂ as a reliable standard gives the total shielding at ¹⁹F in OCF₂ as 236×10⁻⁶. Combining this with the paramagnetic shielding obtained from the ¹⁹F spin—rotation constants gives the diamagnetic shielding as σ^d = 560×10⁻⁶, which is larger than the corresponding ¹⁹F diamagnetic shielding in F₂ of 530×10⁻⁶. The first‐order molecular Zeeman effect was also observed in OCF₂ using a zigzag cell in a magnetic field up to 11 kG giving the diagonal elements of the g‐value tensor along the principal inertial axes of g_aa = | 0.074±0.002 |, g_bb = | 0.038±0.003 |, and g_cc = | 0.028±0.003 |. Arguments are given to suggest that the signs of the g values are all negative, which yields the paramagnetic susceptibility of χ^p = 127×10⁻⁶. The g values are combined with an estimate of the molar susceptibility to yield the average diamagnetic susceptibility in OCF₂ giving a most probable value of ${\mathrm{〈\psi }}^0|{\displaystyle \sum _i}{r}_i^2{\mathrm{|\psi }}^0{\text{〉=47.4×10}}^{\text{−16}}{\mathrm{cm}}^2$ . A theory is presented which allows an estimation of either the molecular g values or the ¹⁹F spin—rotation interaction if one of the two quantities is known. The ¹⁹F parameters obtained in this study may be transferable to other systems. Several low‐J transitions in OF₂ are examined in a 4‐ft liquid‐N₂ absorption cell, and the magnetic properties of ¹⁹F in this molecule are re‐examined.