US 9,703,193 B2  216  215  -continued  O-~-N--~_il_N--0  II  11~1  0  0  F  H  l l  TI  F  F  H  0  0  II  II  o-s-N--S-CF3  a  ~  M  ~:(]  0  0  0  0  O-~-N-_JLCF3  II  0  0  0  O-~-N-_JLCF3  II  0  0  0  0  ~  0-~-N _ _JLCF3.  b--._/  11  0  19.  The onium salt of claim  1,  wherein the onium cation  is selected from the group consisting of an oxonium cation  (R$_{3}$O+), ammonium cation (R$_{4}$N+), pyridinium cation  (C$_{5}$R$_{6}$N+), sulfonium cation (R$_{3}$S+), phosphonium cation  (R$_{4}$ P+), iodonium cation (R$_{2}$I+) and carbonium cation  ((C$_{6}$R$_{5}$ ) $_{3}$C+), wherein R is hydrogen or a straight, branched  or cyclic C$_{1 }$-C$_{20 }$monovalent hydrocarbon group which may  contain a heteroatom.  * * * * *  -continued 