No CrossRef data available.
Published online by Cambridge University Press: 07 August 2017
UV-radiation longward of the Lyman edge (912 Å) can escape from HII-regions. It photodissociates carbon monoxide (λ < 1118 Å) and photoionizes neutral atomic carbon (λ < 1101 Å). The resulting CII/CI/CO transition zone on the edges of molecular clouds (photodissociation region or photodominated region: PDR) has been studied in great detail theoretically (Tielens & Hollenbach, 1985; van Dishoek & Black, 1988; Sternberg & Dalgarno, 1989) and these investigations have recently been extended to cover a wide range of densities and UV-intensities (Burton, Hollenbach & Tielens, 1990; Hollenbach, Takahashi & Tielens, 1991; see also A. Sternberg, this volume).