A HIGH-TEMPERATURE PARTITION-FUNCTION FOR H-3(+)

H-3(+) is the main supplier of electrons to metal-free stars below similar to 8000 K. To describe H-3(+) properly it is important to know its partition function. Previous determinations of this function are based on extrapolations from lower temperatures. A new partition function is presented that is calculated by explicit ab initio computation of levels lying up to 15,000 cm(-1) above the ground state and with J less than or equal to 20. The effect of all other bound levels of H-3(+), which is significant at higher temperatures, is included using a simple model based on Pade approximants. The new partition function is very significantly larger (up to a factor of 100 in some cases) than previous estimates above 3000 K.