The Vibration-Rotation Spectrum of SiH4

The infra-red bands of Si${\mathrm{H}}_4$, measured originally by Steward and Nielsen, have been remeasured at considerably higher resolving power. From a rotational analysis of the bands the equilibrium value of $B$ and values of $B$ for the vibration states ${\nu }_2$, ${\nu }_3$, ${\nu }_4$, ${\nu }_2+{\nu }_3$, and ${\nu }_3+{\nu }_4$ have been determined, $B$ being $\frac{h}{8{\pi }^2\mathrm{Ic}}$. These have, respectively, the values $B_0=3.00\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B^{\prime \prime }=2.96\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B^{\prime }\left({\nu }_3\right)=2.95\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B_{+}^{}{}_{}{}^{\prime }\left({\nu }_2\right)=3.06\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B_{-}^{}{}_{}{}^{\prime }\left({\nu }_2\right)=3.02\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B^{\prime }\left({\nu }_4\right)=2.89\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B_{+}^{}{}_{}{}^{\prime }({\nu }_3+{\nu }_4)=3.05\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B_0^{}{}_{}{}^{\prime }({\nu }_3+{\nu }_4)=2.97\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B_{-}^{}{}_{}{}^{\prime }({\nu }_3+{\nu }_4)=2.94\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B_{+}^{}{}_{}{}^{\prime }({\nu }_2+{\nu }_3)=3.05\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, and $B_{-}^{}{}_{}{}^{\prime }({\nu }_2+{\nu }_3)=2.98\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The centers of the bands have been determined to be the following: ${\nu }_2=974.6\mathrm{}$, ${\nu }_3=2190.6\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, ${\nu }_4=914.2\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $({\nu }_2+{\nu }_3)=3148.8\mathrm{}$, $({\nu }_3+{\nu }_4)=3100.2\mathrm{}$. The value of ${\zeta }_4=\frac{1}{2}-{\zeta }_3=0.454\mathrm{}$ is in good agreement with the value predicted by Jahn for valence force fields. From the band centers the valence force constants are calculated.