US 2020/0133122 Al  7  Apr. 30, 2020  [0068]  In formula (1), n 1  is an integer ofO to 6, with the  proviso that R 1  and R 2  may bond together to form a ring  structure when n$^{1 }$is 1 and R$^{1 }$is not hydrogen. Examples of  the ring thus formed include cyclopropane, cyclobutane,  cyclopentane and cyclohexane rings.  [0069]  Also, two R 1  may bond together to form a ring  structure when n 1  is an integer of at least 2 and R 1  is not  hydrogen. Examples of the ring thus formed include cyclo› propane, cyclobutane, cyclopentane, cyclohexane, norbor› nane, and adamantane rings. When two R  1  bond to a  common carbon atom, two R $^{1 }$may bond together to form a  spiro ring structure with Z.  [0070]  In formula (1),  Q+  is an onium cation. The onium  cation is preferably a sulfonium cation having the formula  (2a) or an iodonium cation having the formula (2b).  (2b)  (2a)  [0071]  In formulae (2a) and (2b),  RH  to R 15  are each  independently a C$_{1 }$-C$_{20 }$ monovalent hydrocarbon group  which may contain a heteroatom. The monovalent hydro› carbon group may be straight, branched or cyclic. Examples  include alkyl groups such as methyl, ethyl, n-propyl, iso› propyl, n-butyl, tert-butyl, cyclopropyl, cyclopentyl, cyclo› hexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexyl› methyl, norbomyl, and adamantyl, alkenyl groups such as  vinyl, ally!, propenyl, butenyl, hexenyl, and cyclohexenyl,  aryl groups such as phenyl, naphthyl, and thienyl, and  aralkyl groups such as benzyl, 1-phenylethyl and 2-pheny› lethyl. Inter alia, aryl groups are preferred. In these mon› ovalent hydrocarbon groups, some hydrogen may be sub› stituted by a moiety containing a heteroatom such as oxygen,  sulfur, nitrogen or halogen, and a moiety containing a  heteroatom such as oxygen, sulfur or nitrogen may intervene  between carbon atoms, so that the group may contain a  hydroxyl moiety, cyano moiety, carbonyl moiety, ether  bond, ester bond, sulfonic acid ester bond, carbonate bond,  lactone ring, sultone ring, carboxylic anhydride or haloalkyl  moiety.  [0072]  Any two of R  11 , R  $^{12 }$and R $^{13 }$may bond together to  form a ring with the sulfur atom to which they are attached.  In this case, examples of the sulfonium cation having  formula (2a) are shown below.  0  oo6cx::o  I  I  I  I  Rl6  Rl6  Rl6  Rl6  -continued  0  II  CX SX)~  S+  #  I  Rl6  CX OX)~  S+  #  I  Rl6  ~  ~sN  I  Rl6  ~  ~sN  I  Rl6  [0073]  Herein R 16  is a C$_{1}$-C$_{20 }$ monovalent hydrocarbon  group which may contain a heteroatom.  [0074]  Examples of the sulfonium cation having formula  (2a) are given below, but not limited thereto. 