Compounds of the formula (I) or (II) wherein R.sub.1 is C.sub.1-C.sub.10haloalkylsulfonyl, halobenzenesulfonyl, C.sub.2- C.sub.10haloalkanoyl, halobenzoyl; R.sub.2 is halogen or C.sub.1-C.sub.10 haloalkyl; Arl is phenyl, biphenylyl, fluorenyl, naphthyl, anthracyl, phenanthryl, or heteroaryl, all of which are optionally substituted; Ar'.sub.1 is for example phenylene, naphthylene, diphonylene, heteroarylene, oxydiphenylene, phenyleneD-D.sub.1-D-phenylene or --Ar'.sub.1-A.sub.1--Y.sub.1-A.sub.1--Ar'.sub.1--; wherein these radicals optionally are substituted; Ae', is phenylene, naphthylene, anthracylene, phenanthrylene, or heteroarylene, all optionally substituted; A, is for example a direct bond, --0--, --S--, or --NR.sub.6--; Y, inter alia is C.sub.1-C.sub.18alkylene; X is halogen; D is for example --0--, --S-- or --NR.sub.6--; D, inter alia is C.sub.1-C.sub.18alkylene; are particularly suitable as photolatent acids in ArF resist technology. ##STR00001##