Knowledge Bank

Pulsed beam Fourier transform microwave spectroscopy was used to investigate the rotational spectrum of the bimolecular complex formed between ozone and acetylene. The reactive gas mixture was sampled with a pulsed solenoid value modified to allow the gases to be led separately into the high pressure side of the orifice through two ports. Two sets of rotational transitions were observed for $O3\dots HC=CH,O3\dots DC=CH$ and $O3\dots DC=CD$. Nuclear spin statistics observed for the $O3\dots HC=CH$, and $O3\dots DC=CD$ isotopes indicate the splitting of the lines arises from internal rotation of acetylene about an axis perpendicular to the -C=C-axis. Both states for the three isotopes were fit to a Watson Hamiltonian giving the following rotational constants (in MHz) for the normal isotopic species: A=9027.483(4) B=2750.606(6) and C=2184.160(6) for the excited state and A=9030.074(3), B=2750.588(8) and C=2184.177(10) for the ground state. Stark effect measurements demonstrated the complex has a plane of symmetry with $\mu a=0.041(1)$ and $\mu c=0.473(1)$ Debyes. Least squares fits of the moment of inertia data were consistent with two structural forms. Rcm. the center of mass separation of ozone and acetylene was found to be 3.251(18){\AA}. $\Theta$, the angle between the local $C2$ axis of ozone and $Rcm$ distinguishes the two forms. The moment of inertia data fit equally well to $\Theta =67(6)\circ$ and $112(6)\circ$.