Theoretical oscillator strengths for infrared electronic transitions of Si2 and SiC

Abstract

Ab initio calculations of the electronic transition moments for all the dipole-allowed systems connecting two valence electronic states of SiC and Si2 have been carried out using multireference configuration interaction wave functions. The <SUP>1</SUP>Sigma(+) diabatic potential curves are found to exhibit an avoided crossing just in the region of equilibrium internuclear separations. The resulting configuration mixing in the Born-Oppenheimer states induces a constructive interference effect that enhances intensities of the d <SUP>1</SUP>Sigma(+) - b <SUP>1</SUP>Pi low-v vibronic transitions both in SiC and in Si2, but not in C2. Ab initio absolute vibronic oscillator strengths and emission probabilities are given for the d-b transitions. The calculated lifetimes of the lowest v prime levels of the d <SUP>1</SUP>Sigma(+) state decrease as v prime increases, especially in SiC. At v prime = 0 they are calculated to be 8.3 microseconds in Si2 and 18.6 microseconds in SiC.