Measurement and Analysis of the ν3 Band of Methane

The ν₃ band of CH₄ has been recorded with a spectral resolution of 0.016–0.019 cm⁻¹ in the region from 2884 to 3139 cm⁻¹. The manifolds containing the allowed lines were subsequently deconvoluted and 198 allowed and 86 forbidden lines were measured and tabulated. Line frequencies and intensities were calculated using the Hamiltonian as extended by Susskind and are listed for the 284 experimental lines which have been assigned. The rms difference in the measured and calculated frequencies for the 211 allowed transitions with upper state $\text{J ≤ 12}$ is 0.0078 cm⁻¹. The 18 molecular constants used to culate the rotation‐vibration fine structure frequencies are compared with previous values and found to have uncertainties which are generally at least an order of magnitude smaller than those given previously.