Knowledge Bank

The spectrum of $\mathrm{<mrow\; data-mjx-texclass="ORD">18</mrow>}O$-enriched water vapor has been recorded between 9000 and $16000cm-1$ using a Fourier-transform spectrometer with a resolution of $0.01cm-1$ and an optical path length of 434 m. The positions of more than 4350 lines have been measured with an accuracy of about $0.0005cm-1$ for strong lines and $0.005cm-1$ for weak lines. During the assignment procedure the lines of 22 bands were observed and the energy levels of the highly excited vibrational states which belong to the first and second decades, and first and second pentadecades of $H218O$ have been determined. Investigated vibrational states $3\nu \{(121),(201),(003),(300),(041),(220),(022),(102),(140)\},3\nu +\delta \{(131),(211),(013),(310),(051),(230),(112),(032),(070)\},4\nu \{(301),(400),(103)\}$. In the energy level calculation we have taken into account the following interactions: 1. The strong bending-rotation coupling leads to the divergence of the Watson-type effective rotational Hamiltonian for vibrational states with high $\nu 2$ values even at moderate values of the rotational quantum numbers $Ka$. For this reason we used the Pade-Borel approximate $method1$. 2. The vibrational states (070) and (160), (080) have been added to the first and second polyads respectively to explain the perturbations due to HEL-$resonances2,3$ in highly excited vibrational states. Rotational, centrifugal distortion and resonance coupling constants have been determined.