EFFECTIVE ROTATIONAL HAMILTONIAN OF THE LOCAL MODE VIBRATIONAL-STATES

The effective rotational Hamiltonians of the local mode states are derived for XY2, XY3 and XY4 molecules by averaging the vibration-rotation Hamiltonians using the corresponding local mode vibrational wavefunctions. The results indicate that in a local mode vibrational state the molecular symmetry is reduced by the coupling of H22 term. A tetrahedral molecule reduces to a C3v symmetric top, a symmetric top becomes an asymmetric top, while the degree of asymmetry increases for an asymmetric top. The vibrational dependences of rotational constants and vibration-rotation coupling parameters predicted by present theory are in good agreement with those obtained experimentally from SiH4 local mode vibrational bands