Argon diluted samples of H2 and ClF were codeposited at 10 K, and no reaction was observed. Photolysis produced a sharp 2834.5, 2832.5 cm−1 doublet, in agreement with (HF)(HCl) dimer from HF and HCl codeposition experiments. Irradiation at 14–16 K markedly increased the mixed dimer and produced weak monomer and dimer bands of HCl and HF, mixed trimer absorptions, and a sharp band at 3857.9 cm−1 for the Cl--HF radical complex. In similar experiments with HD, two mixed dimers, (HF)(DCl) and (HCl)(DF), were formed; likewise, photolyzing D2 with ClF produced two mixed dimers of the form (DF)(DCl) and (DCl)(DF). In the H2 and BrF system, photolysis produced a sharp absorption at 3814.6 cm−1, in agreement with (HBr)(HF) dimer from HBr and HF codeposition experiments, and a new 3830.5 cm−1 band due to the Br--HF radical complex. In a parallel study with HD, two mixed dimers, (HBr)(DF) and (DBr)(HF), were observed while only one mixed dimer, (DBr)(DF), was formed by BrF and D2. In complementary experiments with H2 and Cl2, (HCl)2 was observed at 2818.1 and 2816.2 cm−1.