Anomalous broadening and shifting in D-2 and D-2-He mixtures

Precise and accurate measurements of the Q branch lines of D-2 in D-2 and D -2-He mixtures at several temperatures reveal an anomalous dependence of th e widths and shifts on density. At high densities the widths and shifts are linear in density but with a constant off-set when extrapolated back to ze ro density. At low densities the shifts exhibit normal behaviour, being pro portional to the density. Low density is identified with the free streaming or Voigt region. High density is identified as the usual collision dominat ed regime where the Dicke width is much smaller than the collisional width. It does not appear as if any existing models or theories of isolated lines can explain the present results. (C) 2001 Elsevier Science Ltd. All rights reserved.