Knowledge Bank

The microwave spectra of furan $\cdots H2O$ and furan $\cdots$ DHO were measured and assigned. The spectra contained direct evidence of large amplitude motions (LAMs). In the spectrum of furan $\cdots H2O$, all transitions were split into quartets which were distinguishable as doublets of doublets. The spectrum of furan $\cdots$ DHO was reduced somewhat in complexity with all transitions splilt into doublets. Two dipolar types of trasitions were observed. The presence of quartiets in furan $\cdots H2O$ and DOUBLETS IN FURAN $\cdots DHO$ suggested that there were two LAMs occurring in furan $\cdots H2O$ and that one of these motions was quenched in the complex with DHO. Double resonace was used in both isotopic species in order to distinguish which transitions belonged to the same vibrational state. Each of the six sets of transitions were fitted to the A-reduced Hamiltonian to obtain the effective rotational and centraifugal distoration constants. If the states in furan $\cdots H2O$ are denoted as 1 to 4, then the inertial defects for states 1 and 2 are similar and are approximately -0.34 u {\AA}$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$. For states 3 and 4, $\Delta \approx 0.49$ {\AA}$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$. Similarly, if the two states observed in furan $\cdots$ DHO are denoted as states 5 and 6, than $\Delta =0.319$ and -0.319 and 0.585 u {\AA}$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ respectively. These values for the inertial defects imply a planar of nearly planer compled with significant out-of-plane motions. The amplitude of the motions appears substantially larger in states 3, 4 and 6 compared with states 1,2 and 5, respectively. Further evidence for LAMs in the complex comes from the very large values of $\Delta jk$ and $\Delta k$. Effective structures were fitted from the observed rotational constants. The spectral fetures of this complex, the fitted rotational and centrifugal distoration constants and the effective structures will be presented.