Matt and Cecil are at the University of Arizona, not ASU. Matt, like me, was a student of Cecil's in Renewable Natural Resources. Also, for anaesthetics, Halothane was used until recently, when Isoflourane was deemed a more suitable anaethesia. These are inhaled, NOT injected, and are controlled substances obtainable only by trained individuals, primarily veterinarians. I have never heard of anyone needing to use a dart gun or any similar apparatus to knock down a snake. Which, of course, begs the question: why are you asking about tranquilizer guns to knock out rattlesnakes?
Eric