Figure 1. Methane absorption coefficient at 296K. A. Comparison between experimental and computed spectrum. The computed spectrum is given by the sum of l= 3 (a), l = 4 (b) and double transition (c) components. B. The two components (3, 3) and (3, 4) of the double transition spectrum are shown. The parameters used in the computations are reported in the table (case a).