The magnetic resonance of the NO molecule is observed using the 78-, 79-, and 119-μm lines of the ${\mathrm{H}}_2$O laser as the radiation source. The resonances in three cases are due to the $({}_{}{}^2{}_{}{}^{}\Pi _{\frac{1}{2}}^{}{}_{}{}^{}J=12.5)\to ({}_{}{}^2{}_{}{}^{}\Pi _{\frac{3}{2}}^{}{}_{}{}^{}J=12.5)$, $({}_{}{}^2{}_{}{}^{}\Pi _{\frac{1}{2}}^{}{}_{}{}^{}J=11.5)\to ({}_{}{}^2{}_{}{}^{}\Pi _{\frac{3}{2}}^{}{}_{}{}^{}J=11.5)$, and $({}_{}{}^2{}_{}{}^{}\Pi _{\frac{1}{2}}^{}{}_{}{}^{}J=12.5)\to ({}_{}{}^2{}_{}{}^{}\Pi _{\frac{3}{2}}^{}{}_{}{}^{}J=11.5)$ transitions, respectively. Most of them are magnetic dipole transitions, but a few electric dipole transitions are also observed. It is found that the calculated $g$ factors $g_{c2\mathrm{}}=\left(11.5\right)=g_{d2\mathrm{}}\mathrm{}\left(11.5\right)=-0.0064\mathrm{}$, $g_{c1\mathrm{}}\mathrm{}\left(11.5\right)=g_{d1\mathrm{}}\mathrm{}\left(11.5\right)=0.0272\mathrm{}$, $g_{c2\mathrm{}}\mathrm{}\left(12.5\right)=g_{d2\mathrm{}}\mathrm{}\left(12.5\right)=-0.0092\mathrm{}$, $g_{c1\mathrm{}}\mathrm{}\left(12.5\right)=g_{d1\mathrm{}}\mathrm{}\left(12.5\right)=0.0270\mathrm{}$, and the calculated $\Lambda$-doublet separations $f_{c2\mathrm{}}\mathrm{}\left(11.5\right)-f_{d2\mathrm{}}\mathrm{}\left(12.5\right)=243\mathrm{}$ MHz, $f_{c1\mathrm{}}\mathrm{}\left(11.5\right)-f_{d1\mathrm{}}\mathrm{}\left(11.5\right)=4323\mathrm{}$ MHz, are consistent with our experimental results. The hyperfine structure and the second-order effects are also in agreement with theoretical values. The average separation between the ${}_{}{}^2{}_{}{}^{}\Pi _{\frac{3}{2}}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\Pi _{\frac{1}{2}}^{}{}_{}{}^{}$ states for a given $J$, which we call $X_J$, is found to be 126.4469±0.0005 and 127.5786±0.0005 ${\mathrm{cm}}^{-1\mathrm{}}$ for $J=11.5\mathrm{} \mathrm{and} 12.5$, respectively. The conventional spin-orbit coupling constant is found to be 123.1580±0.0010 ${\mathrm{cm}}^{-1\mathrm{}}$ when $J=12.5\mathrm{} or 11.5$. [The conventional spin-orbit coupling constant $A_c$, commonly referred to as $A$, is given by $A-\delta {(J+\frac{1}{2})}^2+\frac{1}{4}\gamma$ in our notation.] The coupling constant ${\mu }_S$ for the $\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{N}}$ term is found to be -0.006±0.002 ${\mathrm{cm}}^{-1\mathrm{}}$.

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