Is there aspartame in diet pepsi?

Yes, absolutely. Without sugar it seems to be the only substance used as a sweetener these days, although Stevia is starting to come into the picture more.
Source: I've been allergic to Aspartame for 5 years now, I quickly learned how to avoid it. i know Crystal Light has a sweetener called phenylalanine. However i am not sure of it being as good or bad for you as aspartame is..