CO line emission from shock waves in molecular clouds

Calculations are presented of the emission spectrum of rotationally and vibrationally excited carbon monoxide in shocked interstellar molecular clouds. The rotational and vibrational excitation of CO by electrons, H and He atoms, and H2 molecules is discussed, and accurate analytic fits to the rate coefficients of McKee et al. (1982) are presented. The transfer of CO line radiation is treated and a Sobolev-like approximation for radiative transfer in shock waves is developed with allowance for the possibility of population inversions and maser emission. The computation of gas dynamics and level populations is briefly discussed, and graphs are presented of the surface brightness of MHD shocks in various CO lines as functions of shock speed and preshock conditions. The observability of CO maser emission in shocks is considered, and some practical applications of the calculations are pointed out.