Molecular-Beam Magnetic Resonance Studies of HD andD2

The results of some recent molecular-beam magnetic resonance experiments on HD and ${\mathrm{D}}_2$ are reported. A discussion is given of the shifts and distortions of the separated oscillatory field resonance pattern produced by inhomogeneities in the external magnetic field and by the Bloch-Siegert effect. The sign of the electron-coupled spin-spin interaction constant in HD was remeasured to be positive. Its magnitude was determined to be 47(7) Hz. The spectrum of the $J=1\mathrm{}$ state of ${\mathrm{D}}_2$ was observed for external fields less than 160 G, and the spin-rotation and second-rank tensor interaction constants were determined to be $c_d=+8.768\mathrm{}\left(3\right)\mathrm{}$ and $d=+25.2414\mathrm{}\left(14\right)\mathrm{}$ kHz. Using the calculated value $d_M^{\prime }=+2.737\mathrm{}\left(1\right)\mathrm{}$ kHz for the magnetic spin-spin interaction constant, the value of the electric quadrupole interaction constant was determined from the observed value $d$ to be $\frac{\mathrm{eqQ}}{h}=+225.044\mathrm{}\left(24\right)\mathrm{}$ kHz in the first rotational state of ${\mathrm{D}}_2$. Hyperfine transitions were observed for the first time in the second rotational state of ${\mathrm{D}}_2$. The hyperfine constants were determined from the transitions in the limit of zero external magnetic field to be $c_d=+8.723\mathrm{}\left(20\right)\mathrm{}$, $d_M^{\prime }=2.725\mathrm{}\left(14\right)\mathrm{}$, and $\frac{\mathrm{eqQ}}{h}=+223.38\mathrm{}\left(18\right)\mathrm{}$ kHz in the second rotational state. The effects of isotopic substitution and nuclear motion on the hyperfine constants in molecular hydrogen are discussed.