Microwave Absorption Spectra of MnO3F and ReO3Cl

Abstract

The microwave spectra of Mn${\mathrm{O}}_3$F and Re${\mathrm{O}}_3$Cl near 1-cm wavelength have been studied. From the spectra of the first molecule and its isotopic species Mn${\left({\mathrm{O}}^{16}\right)}_2$ ${\mathrm{O}}^{18}$F, the structural parameters were determined as: Mn-O=1.586 A, Mn-F=1.724 A, ∠ (O, Mn, F)=108°27′. The nuclear quadrupole coupling constant of ${\mathrm{Mn}}^{55}$ was measured as $eqQ=16.8\mathrm{}$ Mc/sec. Because of the spin and statistics of ${\mathrm{O}}^{16}$ nuclei not all of the rotational states are allowed. It was found that, whereas in the ground vibrational states only states with $K$ a multiple of three are permissible, in the excited vibrational states of the perpendicular normal modes the states with $K-l$ a multiple of three can occur. For $K=l=\pm 1$ appreciable $l$-type doubling was observed. The amounts of $l$ doubling and their corresponding values of ${\alpha }_v$ were determined for Mn${\mathrm{O}}_3$F. The molecular dipole moment of this molecule was found to be $\mu =1.5\mathrm{}$ Debye units. The hyperfine structure of Re${\mathrm{O}}_3$Cl gives for the ratio of quadrupole moments of the two abundant isotopes of Re a value of $\frac{Q_{{\mathrm{Re}}^{187}}}{Q_{{\mathrm{Re}}^{185}}}=1.067\mathrm{}\pm 0.045$ and for the quadrupole coupling constant of ${\mathrm{Re}}^{187}$, $eqQ=253\mathrm{}$ Mc/sec. This coupling constant and the known optical value of the quadrupole moment of ${\mathrm{Re}}^{187}$ give some information about the electronic structure of the molecular bonds, from which an approximate value of the nuclear quadrupole moment of ${\mathrm{Mn}}^{55}$ was obtained as $Q=0.55\mathrm{}\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$.