Note that the VHCN term was developed to correctly describe the number of vibrational frequencies in the CN reactant (one) and HCN product (four, with degenerated bending modes). The six terms included in Eq. 1 give a very rigid description of this ten-body polyatomic system. Therefore, several switching functions were included to relax the reactive system from reactants (cyano radical + ethane) to products (hydrogen cyanide + ethyl radical). These functions were developed as hyperbolic tangent functions, to ensure smooth changes as the reaction evolves and finally give great flexibility to the PES. In total, the new PES depends on 66 adjustable parameters.