Knowledge Bank

Rotational spectra of the H$2$O-\textit{trans}-HOCO complex have been observed using a Fourier transform microwave (FTMW) spectrometer. The complex was produced in a supersonic jet by discharging a gas mixture of CO and H$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$O diluted in Ar. The observed lines show that the ground state of the complex is split into two by the exchange symmetry of the two equivalent protons of H$2$O. The molecular constants including the hyperfine coupling constants have been precisely determined for the two states. The Fermi contact constants of the two states are smaller than that of the \textit{trans}-HOCO monomer. This result indicates that there is an induced effect for the spin density on the hydrogen nucleus of HOCO by the complex formation.