New scholas will appreciate this piece, which has such a wonderful history and amazing text. It is of medieval origin and has inspired composers for many hundreds of years. Most people today know it from the scene in Amadeus in which Mozart is composing on his last breath. Catholics for hundreds of years couldn't imagine a Requiem or All Souls without it; now it is lost on most everyone -- one sign of a nearly infinite number of signs of what has been lost.
As with all such pieces, the chant is syllabic and can be best presented as sung alternating between high and low voices, with the switch occurring at the double bar.
Here is some history from the Catholic Encyclopedia.
Here is the full sheet music.
And here is a youtube of the chant (but the fancy rhythm stuff is not necessary, and not even desirable).
And here it is as interpreted by Verdi:
