High resolution IR spectra of the linear HCCCN-HCCH and HCN-HCCCCH hydrogen bonded complexes have been obtained using optothermal detection molecular beam techniques. Two vibrational bands have been observed for each complex, which correspond to the terminal "free" C-H stretch vibrations (nu(2)) Of the cyano units and the hydrogen bonded vibrations (nu(3)) Of the acetylenic CH stretches. For both complexes, accurate molecular constants have been Obtained. Furthermore, predissociation lifetimes for the nu(3)=1 states of the both complexes have been determined. The results are compared with those of the linear HCN-HCCH complex obtained by Block et al. [Chem; Phys. 139, 15 (1989)]. 1996 American Institute of Physics.