If you're asking, did they just bomb the cities to see what happened when you drop nuclear weapons on them — there isn't much evidence for that. But getting evidence of that sort was certainly one of the side-benefits of dropping the bombs, and at every stage the scientists were hoping to understand the bombs better as a result of having used them.

There were many motivations for using the bomb, all of which overlapped considerably and were important to many different people who were in on that "decision." These included the standard "end the war quickly" motivation (both to save US lives and keep the Soviets out of the war as much as possible), there were diplomatic motivations (show the Soviets how tough we were, etc.), there were personal motivations (revenge for Pearl Harbor), there were bureaucratic motivations (if you spend $2 billion making two bombs, you have to use them if you don't want to be seen as a failure), there were philosophical motivations (show the world how scary nuclear weapons are, and maybe they will end all wars). You can add scientific interest as a secondary benefit, I think, but I don't think it was a major motivation.