Knowledge Bank

A millimeter-wave spectrometer having a sensitivity of $4\times 10-10cm-1$ in the 2-mm region has been used for observation of the ``forbidden” transitions $J\to J,K=\pm 4\to \pm 1$ and $J\to J,K=\pm 5\to \pm 2$ in $AsH3$. A comprehensive computer analysis was made of the frequencies measured in this work together with available microwave frequencies of other transitions. This analysis provides accurate values of the rotational constants, nuclear quadrupole couplings, and effective structural parameters af the molecule. The spectral constants $BO$ and $CO$ (in MHz) are 112 470.597 and 104 884.665, respectively.