6533b839fe1ef96bd12a6d30

RESEARCH PRODUCT

Line strengths of the ν2 + ν3 and ν3 − ν2 bands of methane (12CH4)

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Abstract The individual linestrengths of two related bands of 12 CH 4 , ν 2 + ν 3 near 4545 cm −1 and ν 3 − ν 2 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 ν 2 + ν 3 and J ′ = 12 in ν 3 − ν 2 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 ν 2 + ν 2 and from 37% to 5.8% with 186 lines of ν 3 − ν 2 . 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 12 CH 4 . Predictions of both bands of 12 CH 4 and ν 2 + ν 3 of 13 CH 4 are available for lines with strengths greater than 10 −6 cm −2 ·atm −1 at 296 K.