Knowledge Bank

Microwave spectra have been obtained for the complexes of water with $CO2\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ and $N2O$ using molecular beam electric resonance. Both complexes are planar with the oxygen of water binding to the center of the linear molecule, such that the heavy atoms form a T-shaped structure. In the $CO2$ complex the water's $C2\nu$ axis is perpendicular to the $CO2$ while in the $N2O$ complex it is tilted away from the a axis by $40\circ$. Internal rotation occurs in both complexes, giving rise to two states with measurably different rotational constants. These differences cause splittings in the microwave transitions of water-$N2O$, however in water-$CO2$ only shifts are observed. (As the internal rotation exchanges the equivalent, zero spin oxygen nuclei of $CO2$ only one internal rotation state is symmetry allowed for a given rotational state.) A recent fit of the transitions of water-$CO2$ giving the rotational constant splittings for the isotopes $H2O$, HDO, and $D2O$ will be presented. This allows for a detailed investigation of the two-fold internal rotation problem and comparison of the symmetric $CO2$ complex with the asymmetric $N2O$ complex. The effects of paths more complex than a rotation about the $C2\nu$ axis of water are examined for water-$N2O$. The interpretation of the centrifugal distortion constants will also be addressed. This is accomplished through a fast, simple implementation of the Eckart conditions to subtract overall rotation from an arbitrary rotation of the subunits.