  I describe DESPOTIC, a code to Derive the Energetics and SPectra of Optically
Thick Interstellar Clouds. DESPOTIC represents such clouds using a one-zone
model, and can calculate line luminosities, line cooling rates, and in
restricted cases line profiles using an escape probability formalism. It also
includes approximate treatments of the dominant heating, cooling, and chemical
processes for the cold interstellar medium, including cosmic ray and X-ray
heating, grain photoelectric heating, heating of the dust by infrared and
ultraviolet radiation, thermal cooling of the dust, collisional energy exchange
between dust and gas, and a simple network for carbon chemistry. Based on these
heating, cooling, and chemical rates, DESPOTIC can calculate clouds'
equilibrium gas and dust temperatures, equilibrium carbon chemical state, and
time-dependent thermal and chemical evolution. The software is intended to
allow rapid and interactive calculation of clouds' characteristic temperatures,
identification of their dominant heating and cooling mechanisms, and prediction
of their observable spectra across a wide range of interstellar environments.
DESPOTIC is implemented as a Python package, and is released under the GNU
General Public License.
