Relationship between the luminosity ratio HCO⁺ to CO (top) and the HCO⁺ velocity width, and the luminosity ratio SiO to CO (bottom) and the SiO velocity width for each molecular cloud of the survey. Open circles denote Galactic center clouds, an asterisk the disk clouds, and filled triangles are clouds that probably are in an intermediate region, influenced by a bar, and that present large linewidth, probably due the strong Galactic center tidal forces in this region. There is a cloud (number 35 in SiO) with a large linewidth (~35 kms^-1) in the bottom plot. This cloud is also not considered in our analysis owing the poor fit (see Fig. E.8).