Models of H3+ in warm, diffuse, molecular gas in the Galactic centre.

Oka et al. (Oka et al. 2005 Astrophys. J. 632, 882-893) have recently observed a large column density of H3+ in the Galactic centre. In one of the gaseous components, a column density of H3+ in its metastable level (3,3) of approximately 4 x 10(14) cm(-2) is measured. From the excitation of H3+, they deduce a density below 50 cm(-3) and a temperature approximately 270 K. In this paper, we report results for this region from a new version of our PDR code which includes the H3+ excitation. Models show it is unlikely that the mean temperature of the gas could be above 100 K. We also show that there is a possibility to produce hot H3+ in C-shocks.