Infrared Absorption Spectra of Phosphine

Abstract

The 10μ absorption region of P${\mathrm{H}}_3$ has been resolved into three bands, a pair with centers at 1121 ${\mathrm{cm}}^{-1\mathrm{}}$ and 992 ${\mathrm{cm}}^{-1\mathrm{}}$ in which the line intervals are approximately 11 ${\mathrm{cm}}^{-1\mathrm{}}$, and a single band at 990 ${\mathrm{cm}}^{-1\mathrm{}}$ with line intervals of approximately 8.5 ${\mathrm{cm}}^{-1\mathrm{}}$. The 4.3μ band has intervals of approximately 8.5 ${\mathrm{cm}}^{-1\mathrm{}}$ and its center is at 2327 ${\mathrm{cm}}^{-1\mathrm{}}$. All apparently have zero branches, as do the two higher frequency bands at 3428 ${\mathrm{cm}}^{-1\mathrm{}}$ and 4541 ${\mathrm{cm}}^{-1\mathrm{}}$. No absorption was observed between 16μ and 22μ. The two parallel type bands may be identified by comparison with the pure rotation spectrum observed by Randall and Wright. They are the ones at 990 ${\mathrm{cm}}^{-1\mathrm{}}$ and 2327 ${\mathrm{cm}}^{-1\mathrm{}}$. The doubling observed in the corresponding bands of N${\mathrm{H}}_3$ does not appear here; hence the phosphorus atom cannot pass readily through the plane determined by the three hydrogen atoms. The perpendicular type bands have intense central maxima, and do not show an intensification of every third line as in N${\mathrm{H}}_3$. This indicates that P${\mathrm{H}}_3$ behaves like a spherical top. The moment of inertia about the axis of symmetry and the interatomic distances cannot be determined precisely until information is available concerning the coupling of rotation and vibration.