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In this work we report the results on the pure rotational spectra of the PD($\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma -$) radicalobtained by using far-infrared laser magnetic resonance (FIR LMR) spectroscopy. The FIR LMR spectrometer used in the present work has recently been constructed at the Institute for Molecular Science. The design of the FIR laser is similar to that described by $Evenson.1$ The PD radical was generated by passing microwave discharged $D2O$ or $D2$ gas over red phosphorus powder at 200 mT pressure. The FIR LMR spectra of PD were recorded with the laser lines of 570$\mu$m, 380$\mu$m, 287$\mu$m, 232$\mu$m, 191$\mu$m and 164$\mu$m for the $v=0 $ state, and 392$\mu$m for the v = 1 state. The doublet hyperfine splittings due to the P nucleus were well resolved in all the observed spectra. The triplet hyperfine splitting due to the D nucleus was observed only for $N,J=3,2\leftarrow 2,1$ transition. Combining the present FIR LMR data with the IR LMR data obtained by Uehara and $Hakuta2$, the molecular constants of the PD($\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma -$) radical were refined, for example, $B\prime \prime$=4.362877 (16)$cm-1$, $A\prime \prime$=2.20829(74)$cm-1$, $B\prime$=4.269241(59)$cm-1$ and $\lambda \prime$=2.2090(14) $cm-1$. We also observed the pure rotational spectra of the $PO2$ an PO radicals in the reaction of microwave discharged $D2O$ and red phosphorus. We report briefly their spectra and the reaction mechanism for generating these radicals.