Infrared spectra of Cl--C2H2 . Ar, Br--C2H2 . Ar, and I--C2H2 . Ar are recorded in the C-H stretch region by monitoring production of X--C2H2 photofragments. Each spectrum exhibits a single band corresponding to the vibration of a hydrogen-bonded C-H unit (nu(HB) = 2882, 2982, 3075 cm(-1) for Cl--C2H2 . Ar, Br--C2H . Ar, I--C2H2, . Ar, respectively). Marked differences between the spectra of Cl--C2H2 . Ar and Cl--C2H2 are attributable to the strong Cl--HCCH bond which prevents cold Cl--C2H2 complexes from dissociating following absorption of an infrared photon. The evidence suggests that addition of the first few Ar solvent atoms has a minor influence on the C-H stretch vibrations of the halide-acetylene complexes. (C) 2003 Elsevier Science B.V. All rights reserved.