van der '''Waals''' damping parameter describes broadening of spectral lines due collisions with neutral particles, e.g. Hydrogen atoms. In VALD3 it can have three values:

if 0: it is not known;

if <0: log γ,,6,, in units of rad/(s&middot;N,,H,,) at l0000 K (where N,,H,, is the number density of neutral Hydrogen atoms in 1/cm^3^);

if >0 : two parameters as defined in Barklem et al. [[https://www.aanda.org/articles/aa/pdf/2002/15/aah3335.pdf|2000A&AS..142..467]]. Integer part is cross-section σ, fractional part is velocity parameter α.