Infra-red cryogenic studies. Part 6.—Deuterium chloride in argon and other matrices
Infra-red spectra are reported of DCl in a variety of matrices at 20 K. At low DCl concentrations, absorptions due to monomeric DCl are observed. Hindered rotation is observed in three matrices which offer spherically symmetrical substitutional sites (Ar, Kr, SF6) and assignments are made to the vibration-rotation lines including R(2) and P(2). The rotational spacing for DCl decreases less from gas to matrix than for HCl as predicted by a rotational-translational coupling model. Rotation is not observed in matrices offering cylindrical substitutional sites (N2, CO2, CO) or in CH4. Matrix-induced frequency shifts show a similar behaviour to those of HCl. A detailed study has been made of the association of DCl in argon matrices and the two dominant multimer bands that arise are assigned to cyclic dimer and cyclic trimer. Further bands assigned to higher multimers agree well with predictions from an intermolecular resonance interaction model, though detailed study of HCl—DCl mixed multimers in argon shows that this model is only fully successful in dealing with trimers and higher multimers. Spectra of binary mixtures of DCl/X in Ar(X = N2, CO2 and CO) show three groups of induced bands arising from DCl—X, (DCl)2—X and DCl—X—DCl interactions. With N2 and CO2 the interactions are thought to be largely electrostatic but CO has a much stronger effect suggesting a specific hydrogen-bond interaction involving the oxygen atom.