The deuterium abundance in QSO absorption systems: a mesoturbulent approach

A new method, based on simulated annealing technique and aimed at the inverse problem in the analysis of intergalactic or interstellar complex spectra of hydrogen and metal lines, is outlined. We consider the process of line formation in clumpy stochastic media accounting for fluctuating velocity and density fields self-consistently. Two examples of the analysis of `H+D’-like absorptions seen at z = 3.514 and 3.378 towards APM 08279+5255 are presented.