Theoretical transition probabilities for the A 1Pi-X 1Sigma+ system of AlNC and AlCN isomers based on global potential energy surfaces

Transition probabilities were evaluated for the X (1)Sigma(+)-A (1)Pi system of AlNC and AlCN isomers to analyze photoabsorption and fluorescence spectra. The global potential energy surfaces (PESs) of the X (1)Sigma(+) and A (1)Pi (1 (1)A("),2 (1)A(')) electronic states were determined by the multireference configuration interaction calculations with the Davidson correction. Einstein's B coefficients were computed by quantum vibrational calculations using the three-dimensional PESs of these states and the electronic transition moments for the X-1 (1)A(") and X-2 (1)A(') systems. Einstein's B coefficients obtained for AlNC or AlCN exhibit that the Al-N or Al-C stretching mode is strongly enhanced in the transition. The absorption and fluorescence spectra calculated for the X-1 (1)A(") and X-2 (1)A(') systems are discussed comparing with the observed photoexcitation and fluorescence spectra. The lifetimes for the several vibrational levels of the A (1)Pi state were calculated to be ca. 7 ns for AlNC and 21-24 ns for AlCN from the fluorescence decay rates of the 1 (1)A(")-X and 2 (1)A(')-X emissions.