The role of excited H2 in protoplanetary disks

This thesis discusses how much influence excited H2 has on different molecular species in the protoplanetary disk. Since H2 contains more energy in its excited state than in its ground state, some reactions that have an activation barrier or are endothermic, can proceed faster with excited H2. The extra energy is used to overcome the barrier. Also, the reaction rate for the reaction H2(v = 1) + C → CH + H is discussed. An Arrhenius equation is used to fit the reaction rate. The ProDiMo code from Woitke et al. (2009) was used to model class II protoplanetary disks surrounding low mass stars. Besides a standard model, four other models were used, one without excited H2, one with an adjusted reaction rate for H2(v = 1) + C, another one had an increased UV flux and the last one was a model of a Herbig Ae/Be star. The masses and the line fluxes of different species were compared in the different models. The influence of excited H2 on CH and indirect on HCO is especially important in this thesis. Boltzmann plots were made for rotational emission lines of CH and the rotational temperature was derived from them. This was compared to an observed rotational temperature for CH. It can be concluded that excited H2 has the largest influence on CH and HCO. In the absence of excited H2, the low rotational lines of CH decreased more in flux than the higher rotational lines. The difference for the low lines should be detectable. For HCO the decrease in line flux is probably too small to be detected. If the UV flux was increased, the masses of CH and HCO became higher, just as their line fluxes. For the Herbig Ae/Be star, this also happened, but the increase was less than with the increased UV flux.