to place an adverb between 'to' and the infinitive of a verb, for example, to say 'to strongly deny a rumour'. Some people consider this to be bad English style.
SPLIT AN INFINITIVE
Meaning of SPLIT AN INFINITIVE in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005