LINE STRENGTHS OF THE NU-2 + NU-3 AND NU-3-NU-2 BANDS OF METHANE ((CH4)-C-12)1

The individual linestrengths of two related bands of 12CH4, ν2 + ν3 near 4545 cm-1 and ν3 - ν2 near 1484 cm-1, were measured with accuracies of 3% and 5%, respectively. In the analysis, an eight-term expansion of the dipole moment through second order was required to fit the strengths of transitions up to J′ = 10 in ν2 + ν3 and J′ = 12 in ν3 - ν2 and to explain the considerable perturbations observed. Application of this model reduced the rms deviations from 68% (zero-order) to 6.3% with the 248 selected lines of ν2 + ν2 and from 37% to 5.8% with 186 lines of ν3 - ν2. The integrated bandstrengths for the two bands, respectively, are 1.84(5) and 0.0085(4) cm-2·atm-1 at 296 K for a 100% sample of 12CH4. Predictions of both bands of 12CH4 and ν2 + ν3 of 13CH4 are available for lines with strengths greater than 10-6 cm-2·atm-1 at 296 K. © 1992.