Hyperfine effects on spectral line shape. II. The case DCO+-He

We discuss the hyperfine effect on the shape of rotational spectral lines of DCO+ broadened by collisions with helium. Hyperfine scattering matrix is calculated by the recoupling technique from the spin-free scattering matrix which is obtained by close-coupling calculations and by a previously tested potential. Line shape is calculated for different rotational transitions, perturber density values, and collisional energies. As forecast by a semiclassical treatment and contrary to what may happen for a symmetric top absorber, hyperfine effects are small for a linear absorber. In our case they are of about 2%. We could also verify that the two hyperfine effects on the line shape, modification of resolved components and collisional coupling between them, cancel each other at high values of helium density when hyperfine structure collapses into a single line. (C) 2011 American Institute of Physics.