Recovered optical depth spectra of the 3.4 μm hydrocarbon band toward sources S7, S10, and S11. The black solid lines are the optical depths deduced from the observations and the associated continua presented in Fig. 2. The deduced underlying 3.47 μm bands (dashed lines) are shown by a Gaussian functions with 0.1 μm FWHM and a maximum depth estimated from the water ice optical depths (cf. Table 3 and text for details). The red thick solid lines are the subtractions of the dashed lines from the black solid lines and represent the 3.4 μm hydrocarbon features. The positions of the subpeaks corresponding to the C-H stretching modes in the 3.4 μm band are indicated by the vertical dotted lines (asymmetric stretch in the methyl and methylene groups at 3.38 and 3.42 μm, and symmetric stretch in the methyl and methylene groups at 3.48 and 3.50 μm, respectively).