Knowledge Bank

Recent experiments have shown that the mechanism of the Stark shift for molecules in region of high state density is complicated at the eigenstate level. Essentially, the eigenvalue position do not show much movement with changing electric-field strength, however, the eigenvector components (and therefore the intensities) vary dramatically with strength. In an attempt to understand this kind of phenomenon we are modelling the influence of the an electric field on the infrared spectrum of HCCF in the region corresponding to five quanta of the CH stretch. Our model considers explicitly four kinds of Fermi resonances plus the off-diagonal {l}-resonance interaction as proposed by Vaittinen $etal1$. The effect of these resonance is to break the Hamiltonian matrix into a series of Fermi polyads. Although the dimension of these submatrices is still large (several thousands) it is possible to reduce their size in a drastic way by using a tier model which only takes into account sequential couplings between the zeroth order states. The electric field destroys the J quantum number, complicating the problem, but it is still possible to reduce the size of the matrices by including the operator $\mu$ E $\cos \theta$ in the tier scheme.