VANDERWAALS COMPLEXES OF CHEMICALLY REACTIVE GASES - OZONE ACETYLENE

A pulsed-beam Fabry-Perot cavity Fourier-transform microwave spectrometer was used to observe rotational spectra of the normal, d1- and d2-isotopic species of the ozone-acetylene van der Waals complex. The work employed a modified, pulsed-solenoid valve which served as a flow reactor to sample the reacting gas mixture of 1% ozone and 1% acetylene in argon. The c-type transitions of the three isotopic species were split into tunneling doublets due to an internal rotation of acetylene which exchanges the hydrogen (deuterium) atoms. Spectral constants of the two tunneling states for each isotopic species were obtained independently from fits to an asymmetric top Watson Hamiltonian. Stark effect measurements for O3-C2H2 gave mu-a = 0.041 (1) and mu-c = 0.473 (1) D. The microwave data show the complex has C(s) symmetry with the molecular axis of acetylene located parallel to the OOO plane of ozone at a center-of-mass separation of R(cm) = 3.251 (2) angstrom. Ab initio calculations at the MP4(SDQ)/6-31G(d,p) level have found the terminal oxygens of ozone are tilted symmetrically toward the molecular axis of acetylene. The combined microwave and ab initio results indicate that the interaction potential surface of ozone plus acetylene is quite similar to ozone plus ethylene at van der Waals distances.