Index of Refraction of Methane in the Infra-Red and the Dipole Moment of the CH Bond

The index of refraction of methane has been measured for 49 different wave-lengths in the infra-red between 1 and $15\mu$. These data have been interpreted in terms of the active infra-red frequencies of methane, and yield what may be considered estimates of the dipole moment of the CH bond and the rate of change of this moment with CH distance. The measurements show that the infra-red bands are only about one-sixth as strong as would be necessary to remove the discrepancy between $n_{\infty }-1\mathrm{}$ as obtained from indices of refraction measured at optical wave-lengths and extrapolated to infinite wave-length, and $\epsilon -1\mathrm{}$ as determined from dielectric constant measurements.