What if there has been an infinite series of gods, each of which gives birth to the next one just before he dies? Is that rational?
What purpose does this question serve?
Here's a better one for you: is it rational to believe that something can spontaneously come from nothing? This is the question whose answer undermines the rationality of your atheism. I don't see any way you can get around it.
And just undermines the rationality of your atheism?