Proton Spin–Lattice Relaxation in HCl–Ar Mixtures

Proton spin–lattice relaxation times have been measured in gaseous HCl as a function of density and in gaseous HCl–Ar mixtures as a function of temperature and composition. Values of $T_1$ have been extracted from the experimental data on mixtures which are appropriate to pure HCl and to HCl infinitely dilute in Ar in the density regions where only binary collisions are important. The spin–rotational interaction provides the the only important relaxation mechanism. Cross sections for changes in rotational angular momentum are estimated for HCl–HCl and HCl–Ar collisions.