H 2 Emission Spectra with New Formation Pumping Models

Abstract

It has been predicted that newly formed on the surface of dust grains should be in highly vibra-H 2 tionally and rotationally excited states in the ground electronic state via the formation pumping mechanism. This suggests that the rovibrational emission spectrum of may be detectable even in regions H 2 without a source of UV pumping or dynamical excitation. Moreover, the infrared emission arising H 2 from formation pumping can be a new probe that will directly show us the spot where the evolution from H I clouds to clouds occurs. In the present work, we investigate the pure e †ects of formation H 2 pumping in infrared emission spectra with our new formation pumping models. We build up our H 2 formation pumping models for newly formed on icy mantles, carbonaceous dust, and silicate dust, on H 2 the basis of the recent progress of basic studies about the formation process on the surface of dust H 2 grains. Then, we calculate the emission spectra with our new formation pumping models, considering H 2 the early stage of an evolving region from H I clouds to clouds dominated by the formation H 2 H 2 process on the surface of dust grains, of uniform H I density cm~3 and the gas temperature n H \ 103 T \ 10 K, in the cold interior of interstellar clouds under a weak ultraviolet (UV) radiation Ðeld. We Ðnd that the resulting infrared emission spectra dominated by formation pumping can be discrimi-H 2 nated from those dominated by UV pumping as well as have information about the property of dust. We also Ðnd that the Ñuxes of the most intense emission lines arising from formation pumping should be strong enough to be detected. In the wavelength range j 1.6 km, if the line intensities of many tran-Z sitions from higher rotational states such as 1È0 S(3), 1È0 S(5), and 1È0 S(7) become stronger than that of the 1È0 S(1) transition, it should be the evidence of emission arising from formation pumping. In H 2 the wavelength range j 1.6 km, if many transitions from higher vibrational states are detected, the [ emission should be originated from newly formed on icy mantles or silicate dust. On the contrary, if H 2 not, the emission should be from formed on carbonaceous dust. H 2 Subject headings : dust, extinction È infrared : ISM È ISM : lines and bands È ISM : molecules È molecular processes