This is from the Rite of Penance #21
In imminent danger of death, it is sufficient for the priest to say the essential words of the form of absolution, namely, “I absolve you from your sins in the name of the Father, and of the Son, and of the Holy Spirit.”
That’s pretty clear. The “essential words” would be another way of saying “the words required for validity.” Now, common sense would have to apply as well. Many priests say “absolve you of your sins” (rather than “from”) simply because it sounds odd in English and it becomes a habit (not an intentional one, but an accidental slip). Also, I do believe that to say “…name of the Father, and the Son…” (omitting “of”) would likewise be valid for the same reason. I’ve never thought about adding the word “God” three times. It sounds akward, but I do not believe that it would affect validity.
I do think that omitting the mention of the Trinity, on the other hand, would affect validity, because that is essential from a theological perspective. It’s not the person of the priest who is absolving, but the priest acting in the name of the Trinity (and of course, in persona Christi, but that’s a different thread). Therefore those words must be spoken.