The Infrared Absorption of Benzene in the Liquid, Solid and Vapor States

The 2.19μ, 2.46μ, and 3.25μ infrared absorption regions of benzene were investigated in the liquid, solid and vapor states with a grating spectrograph whose theoretical resolving power was almost 15,000. For all the bands measured the solid absorption was approximately the same as that of the liquid but with the bands shifted slightly towards longer wave-lengths; the 3.25μ and 2.46μ bands showed a shift of about 13A, and the bands lying in the 2.19μ region showed a shift of about 20A. In the vapor the absorption was quite different from that of the liquid. The 3.25μ region had two strong bands in the vapor, each showing evidences of three components, while the liquid had three bands; interpreting the three components of the vapor bands as the envelopes of the vibration-rotation bands the value, 14×${10}^{-39\mathrm{}}$ g ${\mathrm{cm}}^2$, is obtained for the moment of inertia of the benzene molecule. The 2.46μ region showed a doublet in the vapor while the liquid had a single strong band. The 2.19μ region showed two bands incompletely resolved in the vapor, but the liquid and solid showed a group of five bands with indications of a sixth.