19  US 9,904,167 B2  20  Examples of the organic onium ion (countercation) which  is represented by M$_{1 }$ +  and M$_{2 }$ +  include onium ions such as  iodonium, sulfonium, phosphonium, diazonium, ammo› nium, pyridinium, quinolinium, acridinium, oxonium, sele› nonium, and arsonium, among which onium ions such as  iodonium, sulfonium, phosphonium, diazonium, quino› linium, and acridinium are preferable, and onium ions such  as iodonium and sulfonium are even more preferable.  In addition, examples thereof include cations such as  onium ions of onium salts of group 15 to 17 elements  described in JP1994-184170A (JP-H06-184170A), and the  like, diazonium ions of diazonium salts described in S. I.  Schlesinger, Photogr. Sci. Eng., 18, 387 (1974), T. S. Bal et  al., Polymer, 21, 423 (1980), and the like, ammonium ions  of ammonium salts described in U.S. Pat. No. 4,069,055A,  U.S. Pat. No. 4,069,056A, US RE27992E, JP1991-140140A  (JP-H03-140140A), and the like, phosphonium ions of phos› phonium salts described in D.C. Necker et al., Macromol› ecules, 17, 2468 (1984), C. S. Wen et al., Teh, Proc. Conf.  Rad. Curing ASIA, p. 478 Tokyo, October (1988), U.S. Pat.  No. 4,069,055A, U.S. Pat. No. 4,069,056A, JP1997- 202873A (JP-H09-202873A), and the like, iodonium ions of  iodonium salts described in J. V. Crivello et al., Macromol› ecules, 10 (6), 1307 (1977), Chem. & Eng. News, November  28, p. 31 (1988), EP104143B, EP339049B, EP410201B,  JP1990-150848A  (JP-H02-150848A),  JP1990-296514A  (JP-H02-296514A), and the like, sulfonium ions of sulfo› nium salts described in J. V. Crivello et al., Polymer J. 17,  73 (1985), J.  V. Crivello et al., J. Org. Chem., 43, 3055  (1978),  W.  R. Watt et al., J. Polymer Sci., Polymer Chem.  Ed., 22, 1789 (1984), J. V. Crivello et al., Polymer Bull., 14,  279 (1985), J. V. Crivello et al., Macromolecules, 14(5),  1141 (1981), J.  V. Crivello et al., J. Polymer Sci., Polymer  Chem. Ed., 17, 2877 (1979), EP370693B, EP161811B,  EP410201B,  EP339049B,  EP233567B,  EP297443B,  EP297442B, U.S. Pat. No. 3,902,114A, U.S. Pat. No. 4,933,  377A, U.S. Pat. No. 4,760,013A, U.S. Pat. No. 4,734,444A,  U.S. Pat. No. 2,833,827A, DE2904626B, DE3604580B,  DE3604581B, JP! 995-28237 A (JP-807-28237 A), JP! 996- 27102A (JP-H08-27102A), and the like, quinolinium ions of  quinolinium salts described in JP1997-221652A (JP-H09- 221652A) and the like, selenonium ions of selenonium salts  described in J.  V. Crivello et al., Macromolecules, 10 (6),  1307 (1977), J.  V. Crivello et al., J. Polymer Sci., Polymer  Chem. Ed., 17, 1047 (1979), and the like, and arsonium ions  of arsonium salts described in C. S. Wen et al., Teh, Proc.  Conf. Rad. Curing ASIA, p. 478 Tokyo, October (1988), and  the like; however, the present invention is not limited  thereto.  In addition, preferable examples of the countercation  described above include cations having the structure repre- sented by any one of Formulae (II) to (VII) below.  R 1 -W::::N  +  R 2 -I-R 3  R4  I  s+  Rs/ ’-R6  R7  I  RS-p+-RIO  I  R9  (II)  (III)  (IV)  (V)  -continued  (VI)  (VII)  In Formulae (II) to (VII) above, R 1  to R 3  each indepen› dently represent an aryl group, R 4  to R 6  each independently  represent an alkyl group, an alkenyl group, an alkynyl group,  an aryl group, a cyclic hydrocarbon group, or a heterocyclic  group, R 7  to R 11  each independently represent an alkyl  group, an alkenyl group, an alkynyl group, an aryl group, a  cyclic hydrocarbon group, a heterocyclic group, an alkoxy  group, or an aryloxy group, and R$^{12 }$to R$^{17 }$each indepen› dently represent a hydrogen atom, a halogen atom, or a  monovalent organic group.  The alkyl groups denoted by R 4  to R$^{11 }$preferably have 1  to 30 carbon atoms, more preferably 1 to 20 carbon atoms,  and particularly preferably 1 to 8 carbon atoms, and may be  straight-chain and may have a substituent group.  The alkenyl groups denoted by R $^{4 }$to R $^{11 }$preferably have  2 to 30 carbon atoms, more preferably 2 to 20 carbon atoms,  and particularly preferably 2 to 8 carbon atoms, and may  further have a substituent group.  The alkynyl groups denoted by R $^{4 }$to R $^{11 }$preferably have  2 to 30 carbon atoms, more preferably 2 to 20 carbon atoms,  and particularly preferably 2 to 8 carbon atoms, and may  further have a substituent group.  The aryl groups denoted by R $^{1 }$to R $^{11 }$preferably have 6 to  30 carbon atoms, more preferably 6 to 20 carbon atoms, and  particularly preferably 6 to 10 carbon atoms, and may  further have a substituent group.  The cyclic hydrocarbon groups denoted by R 4  to R 11  preferably have 3 to 30 carbon atoms, more preferably 3 to  20 carbon atoms, and particularly preferably 3 to 10 carbon  atoms, and may further have a substituent group.  The heterocyclic groups denoted by R 4  to R$^{11 }$preferably  have 4 to 30 carbon atoms, more preferably 4 to 20 carbon  atoms, and particularly preferably 4 to 10 carbon atoms, and  may further have a substituent group. In addition, the hetero  atom included in the heterocyclic group is preferably a  nitrogen atom, an oxygen atom, or a sulfur atom.  The alkoxy groups denoted by R $^{7 }$to R $^{11 }$preferably have  1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms,  and even more preferably 1 to 8 carbon atoms. In addition,  the alkoxy groups may have a substituent group described  below, and the alkyl moiety of the alkoxy groups may be an  alkenyl group, an alkynyl group, a cyclic hydrocarbon  group, or a heterocyclic group other than an aromatic group.  The aryloxy groups denoted by R $^{7 }$to R $^{11 }$preferably have  6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms,  and even more preferably 6 to 10 carbon atoms. In addition,  the aryloxy groups may have a substituent group described  below, and the aryl moiety of the aryloxy groups may be an  aromatic heterocyclic group.  In Formula (III), R 2  and R 3  may be bonded with each  other to form a ring if this is possible.  In Formula (IV), two or more ofR 4  to R$^{6 }$may be bonded  with each other to form a ring if this is possible. 