Bilitrium is a rare element. When combined with an antimatter converter, this crystalline element becomes an incredible source of energy. Thimaldicide gas is a by-product of this conversion.
In the same year, the USS Cantabrian (NCC-24705) team traced the path of the Myhr'an planet killer by a leaking trail of thimaldicide gas. (Star Trek: The Cantabrian Expeditions: "Catalyst, Part One")