Gaussian16 TS-optimization of TS4 (16->17)  at the 
 #temperature=278 freq opt=(TS,noeigentest,calcfc) empiricaldispersion=
 gd3 PBEPBE/6-31g(d,p) scrf=(Read,PCM,solvent=water)
level of theory. Epsilon adjusted to 144.8 to match that of HCN at 278 K.
n3_000 is most stable. 
