Université Paul Sabatier - Bat. 3R1b4 - 118 route de Narbonne 31062 Toulouse Cedex 09, France


Accueil > Publications > Publications par année > Année 2009

Ab-initio study of valence and Rydbeg states of CH3Br.

We performed configuration interaction ab initio calculations on the valence and 5s, 5pa1, and 5pe Rydberg bands of the CH3Br molecule as a function of the methyl-bromide distance for frozen C3v geometries. The valence state potential energy curves are repulsive, the Rydberg state ones are similar to the one of the CH3Br+ ion with a minimum at short distance. One state emerging from the 5pe band has valence and ion-pair characters as distance increases and the corresponding potential curve has a second minimum at large distance. This state has a very strong parallel electric dipole transition moment with the ground state and plays a central role in UV photon absorption spectra. It is also responsible for the parallel character of the anisotropy parameters measured in ion-pair production experiments. In each band, there is a single state, which has a non-negligible transition moment with the ground state, corresponding to a transition perpendicular to the molecular axis of symmetry, except for the 5pe band where it is parallel. The perpendicular transition moments between ground and valence states increase sharply as methyl-bromide distance decreases due to a mixing between valence and 5s Rydberg band at short distance. In each band, spin orbit interaction produces a pair of states, which have significant transition moments with the ground one. In the valence band, the mixing between singlet and triplet states is weak and the perpendicular transition to the math1 state is dominant. In each Rydberg band, however, spin-orbit interaction is larger than the exchange interaction and the two significant transition moments with the ground state have comparable strengths. The valence band has an additional state (math0) with significant parallel transition moment induced by spin-orbit interaction with the ground state at large distance.

Voir en ligne : J. Chem. Phys. 130, 244306 (2009)