Known problems with Cloudy

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Molecular opacities in dust-free environments

Most molecular environments are also dusty. This assumption is behind nearly all ISM chemistry codes (see the comparison given in Roellig et al. 2007, available here). Cloudy includes a complete treatment of x-ray opacities for all elements in grains and molecules, and a detailed treatment of opacity for H-, and H2, and CO. But the code follows the UMIST approach for minor molecules. This includes writing many molecular photo rates as a function of the incident radiation field and the total dust extinction. The opacity contributed by minor molecules is ignored.

The innermost regions of dense disks may be molecular and, if hot enough, dust free. The code is not now applicable to this environment. Species such as TiO may become important opacity sources.

This is on our to-do list and may be included in the next major release. But for now, the code is not applicable to dust-free molecular clouds when minor molecules are important opacity sources.

Many thanks to Andrea Isella for pointing out this problem.

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