for the title reaction and with the results for the reaction with methane. In sum, all the results reported that the HCN product appears vibrationally excited in the bending states, the discrepancy remaining in the percentage. In order to explain the theory/experimental discrepancies different causes were analysed following the arguments developed in our previous work where the description of water product in polyatomic OH + XH  H2O + X (X ≡ D, Br, NH2 and GeH3) reactions was analysed. As a first factor to explain the bending excitation, Bethardy et al. and Nizamov et al. pointed out the relation with the bending potential of the NC…H…R geometry in the linear transition state, R CH3 or C2H5: soft transition states will yield more bending excitation. Now, we have quantitatively analysed this suggestion for the CN + methane and ethane reactions. Figure shows the variation of the energy as a function of the NC…H'…R bending angle in the saddle point for both reactions using analytical surfaces from our lab, PES-2023, for the ethane reaction (present work) and PES-2017 for the methane reaction. Both reactions present similar behaviour, showing soft transition state structures, small dependence with the bending angle, and differences between them of only 0.05 kcal mol -1 at an angle deviation of 30º with respect to the saddle point geometry.