US 2020/0159115 Al  52  May 21, 2020  [0134]  In formulae (la) and (1 b ),  Mq+  is an onium cation.  Onium cations having the formulae (2a ), (2b) and (2c) are  preferred.  [0135]  Herein Rq 11  to Rq 19  are each independently a  C$_{1 }$-C$_{20 }$monovalent hydrocarbon group which may contain a  heteroatom. Any two of Rq$^{11 }$to Rq$^{13 }$may bond together to  form a ring with the sulfur atom to which they are attached.  Rq$^{14 }$and Rq$^{15 }$may bond together to form a ring with the  iodine atom to which they are attached. Any two ofRq$^{16 }$to  Rq$^{19 }$may bond together to form a ring with the nitrogen  atom to which they are attached. The monovalent hydrocar- -continued  H  HO  H  0  F  (2a)  (2b)  (2c) 