Chemical heating of interstellar clouds

The formation and destruction of molecules provides a mechanism for extracting energy from the interstellar radiation field and converting it into thermal energy. The chemical heating sources arising from chemical cycles involving CH2 + and OH are estimated. The CH2 + cycle is a larger source than the H2 formation and destruction source in regions where the hydrogen is largely molecular. The OH cycle may enhance the cosmicray heating rate by a factor of about 3, depending upon the rate coefficients of the various reactions. Subject headings: interstellar matter - molecules, interstellar - nebulae