SPECTRAL INTENSITIES IN THE NU-3-BANDS OF (CH4)-C-12 AND (CH4)-C-13

Relative and absolute line intensities for the ν3 bands of the 12C and 13C isotopic varieties of methane have been measured using a tunable difference-frequency laser spectrometer. From these data the integrated band strength of 13CH4 is calculated to be 0.983 ± 0.007 that of 12CH4, with the uncertainty representing three standard deviations. The absolute ν3 bandstrength for 12CH4 is 266.1 ± 3.0 cm-2 atm-1 at 294.7 K where the errors are dominated by the pressure measurement. This band strength corresponds to an effective transition moment 〈μ3〉 = 0.0534(3) D for 12CH4 from which the ν4 band dipole moment and the Herman-Wallis F factor can be estimated using a recent force field model for methane. © 1979.