DETERMINATION OF THE STRUCTURE OF $H_{2}CO CO_{2}$.

Author Institution: Department of Chemistry, Wesleyan University; Molecular Spectroscopy Division, National Bureau of StandardsThe rotational spectrum of the $H_{2}CO CO_{2}$ van der Waals complex has been measured using a pulsed beam Fourier transform microwave spectrometer. Each rotational line is split into a ``strong'' and ``weak'' intensity component due to the internal rotation of the formaldehyde moiety about its $C_{2}$ axis. The ``strong'' transitions are assigned to a B symmetry internal rotor state with the rotational constants $A=10.399.1(2) MHz, B=2678.215(1) MHz$, and $C=2128.340(1) MHz$. The ``weak'', or A state lines were assigned with the rotational constants $A=10,400.5(2) MHz, B=2678.271(1) MHz,$ and $C=2128.312(1) MHz$. The complex has a planar structure analogous to the ``near slipped parallel'' structures of $(CO_{2})_{2}$ and $CO_{2} OCS$, with the oxygen of $H_{2}CO$ interacting with the carbon of $CO_{2}$. The structural parameters and dipole moments of both the A and B states are the same within the stated uncertainites. The C-O (formaldehyde)-C (carbon dioxide) angle is $102.90(5)^{\circ}$, the O (formaldehyde)-C-O (carbon dioxide) angle is $83.23(3)^{\circ}$, and the O (formaldehyde)-C (carbon dioxide) distance is 2.980(1) A. The measured dipole moments are $\mu_{a} = 1.661(2) D$, and $\mu_{b}=1.671(2) D$