A CHEMICAL STUDY OF THE HOT AND DENSE MOLECULAR GAS ADJACENT TO PHOTODISSOCIATION REGIONS openParPDRSclosePar

we propose to observe a sample of high excitation molecular lines in a strip crossing the photodissociation regions (pdr) associated with ngc 7023, and ngc 2023. since most of the hyperfine atomic lines, and high excitation molecular lines cannot be observed from ground based observatories, the chemical composition and physical conditions of these regions are far from being understood. the central programme includes observations of atomic and h2 rotational lines towards these reflection nebulae. but the rotational lines of molecules like oh, ch, ch2 or nh3 are not included at all. these lines are expected to be strong enough to be detected with iso in a reasonable period of time, and the observation of these molecular lines is essential: 1) to estimate the abundance of these light molecules in the hot gas that constitutes the interface between the atomic and the molecular phases, 2) to determine the physical conditions of this hot molecular gas, and then 3) to understand the cooling mechanisms in these pdrs. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]