Left: average differential ionization rate for different assumed gas column densities along the line of sight N1 and solar abundance. Right: predictions for the photoionization rate are shown by the solid and dashed red lines (for the cloud with solar abundances and the abundances of the NE source, respectively). Observational data taken from Vaupré et al. (2014) are presented as filled circles (measurements) and filled triangles (lower limits). The shaded region indicates a reference range of values of the ionization rate which has been used to constrain the CR spectrum (see text).