I think you're looking for 'excommunicated latae sententiae, which means 'automatically.'
Latae sententiae excommunication only occurs for very specific offenses: apostatsy, heresy, schism, procurement of abortion, sacrilege against the Eucharist, using force against the Pope, consecrating a Bishop without Papal mandate, accepting such consecration, and violation of the Seal of Confession are specifically listed as latae sententiae excommuicable offenses.