Gaussian16 TS-optimization of TS1 (2->3)  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.
TS1_1 is the most stable TS
