If you use any threat at all to make the clone do the work, that's irrational, because you obviously weren't truly of the opinion that one of you should do the work, or even of the opinion that the cloned one should do it. So you were fighting against yourself in your mind before you began the experiment.
If on the other hand both of you are cool with it, the evaporation isn't murder.
If on the other hand both of you are cool with it, the evaporation isn't murder.