http://www.fact-index.com/e/ex/excommunication.html(Notice that abortion is listed, but not rape or murder!)
Roman Catholicism
Excommunication is considered automatic for some sins within the Roman Catholic but can also be a formal affair, generally reserved for renegade clerygymen and such.
The word literally means "out of communion"; the outward sign of this loss of community involves barring the person from participating in Communion, i.e., receiving the Eucharist, and as a consequence losing their status as members of the church. Certain other rights and privileges normally resulting from membership of the church are revoked. Excommunication is often intended to be only temporary, a "medicinal" procedure intended to provoke repentance. In the Roman Catholic church excommunication is usually terminated by repentance and absolution. For minor excommunications the absolution may be pronounced by a confessor (a Priest). More serious offences must be absolved by a more senior official.
Automatic excommunication
There are seven sins for which Roman Catholics are automatically excommunicated:
Apostasy, Heresy, or Schism
Desecration of the Eucharist
Physical force against the Pontiff
One who actually procures an abortion and all accomplices
Priest who absolves a partner in adultery
Priest who directly violates the sacramental seal of confession
Both parties to the consecration of a bishop without a pontifical mandate
SNIP