Can Diet Coke kill sperm cells?

If you plan on flushing your vagina with Diet Coke after sex with a male as an inexpensive means of Birth Control, it's probably not worth the risk. The acidity of the female vagina instantly kills 25% of sperm on contact. Another 20% of sperm are defected anyway. That leaves 55% of sperm under the influence of diet coke. Fun to think about in theory but too risky for birth control as far as I can tell. What happens if that sperm under the influence of diet coke makes it to the egg and fertilizes it. Are you sure you want a child that is 2/3 human and 1/3 Aspartame?