H3+ IN THE EARLY UNIVERSE

Abstract

The chemistry, and radiative and collisional interactions of H3 in the early Universe are examined. The object of study is to investigate whether H3 is essential in cooling of the primordial gas and thus in the formation of the first stars. The consensus so far is overwhelmingly negative. Most previous papers ignore the possibility at the onset because of the very low concentration of H3 , about 10 −9 of H2 or less. Since the dipole infrared emission of H3 is (λ/a) 2 ∼ 10 (λ wavelength: a molecular size) times faster than the quadrupole emission of H2, however, there is a possibility that H3 is comparably efficient coolant as H2. Glover and Savina was the only paper which took this possibility into account. They negate the contribution of H3 because at a gas density higher than 10 cm−3 H3 number density is further reduced by endothermic reaction H + 3 + H → H2 + H + 2 . We will examine this. We will consider the following two effects which have been neglected by the previous workers: (1) the effect of collision which convert translational energy of the gas into the energy of vibration and rotation of the molecules and (2) the effect of spontaneous emission between rotational levels. We find H3 can be a more efficient coolant than H2 in the early Universe depending on temperature, density, and cosmological conditions of the primordial gas at the time of star formation.