MRCI studies on ground and excited states of CBr

Abstract

Potential curves and spectroscopic constants for a large number of doublet and quartet states of CBr were obtained by multireference configuration interaction calculations, using valence triple-zeta basis sets with polarization and diffuse functions. Besides the X2Π ground state, 14Σ−, 12Δ and 22Σ+ have been found to be stable. Spectroscopic constants calculated for 12Δ are in excellent agreement with experimental values obtained by Dixon and Kroto in 1963. Their observed predissociation of one component of 12Δ can be explained by the crossing of the 12Δ potential near equilibrium by 12Σ+. The 12Σ+ state is calculated to have a shallow long-range minimum at 2.31 Å. The dissociation energy of X2Π is calculated to be 3.43 eV. An observed T e of 4.97 eV for 22Σ+ agrees with the theoretical value. Several Rydberg states of the 2π→Ryd and 3σ→Ryd series, starting at T e = 5.25 eV, were identified. Photodissociation of CBr by sunlight, important in the ozone cycle, can occur via direct dissociation of the ground state, or by excitation to 12Δ followed by predissociation. Most dissocative repulsive states lie at higher energies, and are not expected to participate in the photodisscociation of CBr.