Is it stipulated, for a divorce to take effect by linguistic utterance, that the letters be fully and accurately pronounced, especially given that the questioner feels as if he uttered the word "divorce" even though his tongue did not move?

Since the questioner is afflicted with waswas (obsessive whispering), his divorce does not take effect even if he utters it, because the certainty of the marital bond remaining is not affected by doubt regarding divorce. The cure for waswas is to turn away from it, frequently remember Allah, seek refuge in Him from Satan, perform Ruqyah (definition) Shari’ah (Islamic exorcism), and avoid asking questions and searching for fatwas (religious edicts) concerning divorce for those afflicted with waswas.