Radiative lifetimes of vibrational levels and transition probabilities of spontaneous emissions of the six lowest-lying triplet states of AlN radical

The potential energy curves of 23 states of AlN radical are calculated to accurately determine the first several lowest-lying singlet and triplet states. The calculations are done using the CASSCF method, which is followed by the valence internally contracted MRCI approach. The rotationless radiative lifetimes of the vibrational levels are approximately 10−7–10−8 s for the C3Π, D3Π, and E3Δ states, 101–10−4 s for the A3Σ− state, and 10−4–10−5 s for the B3Σ+ state. The origins of the vibronic bands and the radiative lifetimes agree well with the available experimental and other theoretical results. The Einstein coefficients of many vibronic emissions are large for the C3Π–X3Π, C3Π–A3Σ−, D3Π–X3Π, D3Π–A3Σ−, and E3Δ–X3Π transitions and therefore, these transitions are strong. The emissions of the E3Δ–D3Π system are so weak that it is difficult to measure them through spectroscopy. The spectral distribution of the vibronic emissions is evaluated for the transitions of 12 pairs of states. In terms of the radiative lifetimes and transition probabilities obtained here, several spectroscopic routines for observing these states via spectroscopy are proposed.