Molecular beam infrared spectroscopy of the HCCCN–HCCH and HCN–HCCCCH van der Waals complexes.

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 ν[SUB2])of the cyano units and the hydrogen bonded vibrations (ν[SUB3])of the acetylenic CH stretches. For both complexes, accurate molecular constants have been obtained. Furthermore, predissociation lifetimes for the ν[SUB3] = 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)]. [ABSTRACT FROM AUTHOR]