Molecular dispersal

Molecular dispersal was a means by which bodies were disposed of. It was notably a method of execution in Time Lord society. The subject would have his molecules dispersed across time and space to such a wide degree that the body and consciousness could not be reformed.

The Imperiatrix Pandora was dispersed for reshaping history to suit her wishes. The deed was thorough enough that memory of her was purged from history, though her existence was whispered in legend. Part of her consciousness managed to reform in the Matrix, and she attempted to take the position again during the Gallifreyan Civil War. (AUDIO: Imperiatrix)

Lord President Morbius was dispersed for attempting to conquer a large part of the galaxy with his followers. The deed was incomplete, though, since Morbius' brain was saved from dispersal, along with his consciousness. (TV: The Brain of Morbius)

The Fifth Doctor was sentenced to dispersal by the High Council as a means of preventing the return of Omega to Normal Space. However, Omega managed to intercept the Doctor a split second before dispersal took place, and deposit him in the Matrix instead. (TV: Arc of Infinity)

Zygon technology afforded molecular dispersal capabilities remotely. After Madra was killed, Broton dispersed the corpse in order to prevent it falling into the hands of UNIT. (TV: Terror of the Zygons)

Similar devices
This method appeared to be very similar to the effects of the Oubliette of Eternity. However, the Oubliette was thorough enough to completely eliminate all traces and memory of the dispersed subject, and the Oubliette would project that subject into the Antiverse as a side-effect. Knowledge of molecular dispersal was also quite public, while the Oubliette was a closely-held secret of the Celestial Intervention Agency. (AUDIO: Neverland)

Another form of Gallyfreyan execution, with a similar outcome, was vaporisation. (TV: The Deadly Assassin et. al.)