Does a divorce take effect with the statement, "I have divorced Shayma," even if there was no intention of divorce, especially given that the speaker tried to stop himself after beginning the word?

This phrase is not an explicit declaration of divorce, and the term "release" (طلاق) and its derivatives are not explicit. Even if you uttered an explicit declaration of divorce due to obsessive thoughts (waswasah) and without conscious choice, your divorce is not effective. The entire matter is nothing but obsessive thoughts, and nothing results from them. Therefore, turn away from these obsessive thoughts and do not pay attention to them, because indulging them leads to evil and tribulation, and turning away from them is the best remedy.