H3+ recombination and bistability in the interstellar medium

G. Pineau des Forets & E. Roueff
H. DEAC, Oberservatoire de Paris, France

H3+ has recently been detected using infrared absorption towards several dense clouds. On the other hand, we have shown that models of interstellar chemistry could exhibit several stable steady-states. This is due to the non linear behaviour of the chemical equations where H3+ plays a major role. We will investigate the influence of various astrophysical parameters which control the evolution and the final state of the gas such as the density, the cosmic ray ionisation rate, the elemental depletions and the H3+ dissociative recombination rate (which is a key reaction). We will show that these parameters lead to bistability for a range of physical conditions appropriate to interstellar clouds and discuss more specifically their influence on the H3+ abundance in dark clouds. Both steady state and evolution aspects will be discussed.