Catechism of the Catholic Church §1035 — excerpt
The teaching of the Church affirms the existence of hell and its eternity. Immediately after death the souls of those who die in a state of mortal sin descend into hell, where they suffer the punishments of hell, "eternal fire."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: DS 76 · 409 · 411 · 801 · 858 · 1002 · 1351 · 1575 · Paul VI, CPG # 12