Structure of Stationary Photodissociation Fronts

摘要: The structure of stationary photodissociation fronts is revisited. H_2 self- shielding discussed, including the effects line overlap. We find that overlap important for N(H_2) > 10^{20} cm^{-2}. compute multiline UV pumping models, and compare these with simple analytic approximations self-shielding. The overall fluorescent efficiency front obtained different ratios chi/n_H (where chi characterizes intensity incident UV) dust extinction laws. optical depth tau_{pdr} to point where 50% H molecular found be a function dimensionless quantity phi_0 depending on chi/n_H, rate coefficient formation grains, opacity. PDR also depends primarily 10^4K, but shows some sensitivity v-J distribution newly-formed H_2. 1-0S(1)/2-1S(1) 2-1S(1)/6-4Q(1) ratios, ortho/para ratio, rotational temperature in $v$=1 $v$=2 levels are computed as functions density, values n_H. We apply our models reflection nebula NGC 2023. best able reproduce observations having chi=5000, n_H=10^5 cm^{-3}.