Before finishing this Section, we consider it of interest to make a comparison with the "cousin" CN + CH4 reaction, which will permit us to analyse the first alkanes of the series. In 2017 our group developed an analytical potential energy surface, PES-2017, describing this gas-phase reactive process, and the results are presented here. Table compares important properties for both reactions and Figure (lower panel) also includes the contour plot for the methane reaction. The reaction of the CN radical with both alkanes shows a similar topology, with a weak complex in the entrance and a stronger complex in the exit channel. However, the reaction with methane presents a higher barrier (2.5 versus 0.23 kcal mol -1 ) associated with a larger imaginary frequency at the saddle point and with a lower exothermicity. In consequence, the reaction with methane presents a thinner barrier, and a larger tunnelling contribution was observed, which is practically negligible in the reaction with ethane. The small stability of the reactant complex, which produces a practically flat entrance valley, is due to the smaller dipolar moment of the CN radical, (1.450 Debye) as compared with the OH radical (1.668 Debye) in reactions with methane and ethane, which presented more stabilized intermediate complexes.