We report integral, differential and momentum transfer cross sections for elastic scattering of low-energy electrons by several isomers of the C 4 H 8 molecules, such as isobutene, trans-2-butene, cis-2-butene, skew-1-butene and syn-1butene, and by two isomers of C 4 H 10 , the isobutane and the butane molecules. To calculate the cross sections, we use the Schwinger multichannel method with pseudopotentials (Bettega et al 1993 Phys. Rev. A 47 1111) applied at the static exchange level of

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... mation for incident energies from 10 to 50 eV. Although the C 4 H 8 isomers have different geometric structures, our results show that the integral cross sections for each of these isomers present a broad shape resonance around 10 eV; our results also show that for all C 4 H 8 molecular targets, integral cross sections are very similar in shape and magnitude. Similarities are also found in the momentum transfer and in the differential cross sections of these isomers. The same pattern is found in the cross sections of the C 4 H 10 isomers. Through comparison of the integral and momentum transfer cross sections of 1,3-butadiene (C 4 H 6 ), trans-2-butene (C 4 H 8 ) and butane (C 4 H 10 ), all belonging to the C 2h group and having similar structures, we discuss the role of the hydrogen atoms in the scattering process by these molecules. Further we show that the integral elastic cross sections of all simple hydrocarbons present strong similarities after a scaling. We present a simple geometric model for this scaling that works quite well for a whole family of C n H m molecules (with combinations of n = 1, 2, 3, 4 and m = 2, 4, 6, 8, 10).