Does divorce take effect without the intention of divorce, if a person utters "my wife is divorced" while thinking of a previous oath of divorce, in order to overcome the obsessive whispering of repeating the opening Takbir (Allahu Akbar) of prayer?

Divorce does not occur by an inner monologue without uttering it. And if the person afflicted with waswas (obsessive whispering) utters it while overcome and not in control of his mind, then his divorce is not effective. As long as you uttered the divorce due to being overwhelmed by waswas without awareness or choice, then your divorce is not effective. Do not pay attention to intrusive thoughts and doubts, for indulging waswas leads to evil and tribulation, and ignoring it is the best cure for it.