Knowledge Bank

A Hamiltonian taking explicitly into account both Fermi and Coriolis interactions has been set up for triatomic molecules of symmetry $Cs$ and used to reproduce very satisfactorily the available rotational energy $levels1,2$ of the $\{(100),(020)\}$ interacting states of HDO, providing us with realistic wavefunctions as well as precise rotational constants and vibrational energies. Then, to calculate line intensities, these wavefunctions were used together with suitably chosen transition moment operators expanded up to degree 2 in $J\to$ and having the correct symmetry in the $Cs$ group, leading to hybrid bands of both A- and B- type. Using this formalism, it has been possible to determine, from the fit of the existing experimental $intensities1$, the coefficients appearing in the expansions of the transition moments operators of the $2\nu 2$ and $\nu 1$ bands of HDO. In this way, we have improved upon the F-factor formalism which needs much more parameters to reproduce the line intensities with the same precision. Finally, using the transition moments as well as the wavefunctions and energy levels deduced from the diagonalization of the Hamiltonian matrix, we have calculated the whole spectrum of the $\nu 1$ and $\nu 2$ bands of HDO.