Rachmaninov was fascinated by the Dies Irae melody: he makes a musical reference to it in the majority of his compositions.
Rachmaninov was fascinated in the Dies Irae melody: he makes a musical reference to it in the majority of his compositions.
Rachmaninov was fascinated by the Dies Irae melody: he makes a musical reference to it in the majority of his compositions.
Rachmaninov was fascinated in the Dies Irae melody: he makes a musical reference to it in the majority of his compositions.
As a passive verb or participle, "fascinated" idiomatically takes the preposition "by", as do most other passive verbs and participles. It can also take "with," but it can never take "in."