Emission by collisional H2-He pairs at temperatures from 2 to 20 kK

The dipole surface of H-2-He collisional pairs is computed from first principles for 20 intramolecular spacings of the H-2 molecule, from 0.6 to 4 Bohr; 11 separations of the H-2-He pair, from 2 to 6 Bohr; and five values for the angle subtended by the intramolecular and intermolecular axes. From this dipole surface, the dipole matrix elements are obtained for all possible rotovibrational transitions \vJ >--> v'J'>, with v and v'=0,... ,14. Subsequently, the collision-induced emission spectra are computed for frequencies from 100 to 100 000 cm(-1), at temperatures of thousands of Kelvin-a range believed to be important for various light sources of high gas densities, such as the atmospheres of "cool" stars, shockwaves, flames, rocket jets, etc. We find that at the lower temperatures considered, radiation is emitted mostly in the fundamental band of H-2, while at high temperatures the collision-induced emission spectra extend into the visible, with overtone transitions involving large Delta v=v-v'. (C) 1999 American Institute of Physics. [S0021-9606(99)30638-3].