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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. This paper calculates the potential energy curves, spectroscopic parameters, transition dipole moments, and transition probabilities of the AlN radical. The rotationless radiative lifetimes of the vibrational levels are of the order of 10−7 to 10−8 s for the C3Π, D3Π, and E3Δ states, 10−4 to 10−5 s for the B3Σ+ state, and 101 to 10−4 s for the A3Σ− state. The lifetimes of the C3Π, D3Π, and E3Δ states are almost determined by the C3Π–X3Π, D3Π–X3Π, D3Π–A3Σ, and E3Δ–X3Π systems, respectively. Overall, the C3Π–X3Π, C3Π–A3Σ−, D3Π–X3Π, and E3Δ–X3Π transitions, followed by the D3Π–A3Σ− and D3Π–C3Π transitions; the emissions are weak for the A3Σ−–X3Π, D3Π–B3Σ+, and E3Δ–D3Π systems. Curves of the TDM versus internuclear separation of 5pairs of states of the AlN. Unlabelled Image • Lifetimes are of the order of 10−7–10−8 s for the C3Π, D3Π, and E3Δ states. • C3Π–X3Π, C3Π–A3Σ−, D3Π–X3Π, D3Π–A3Σ−, and E3Δ–X3Π transitions are strong. • Lifetimes are 101–10−4 s for the A3Σ− state and 10−4–10−5 s for the B3Σ+ state. • Vibronic emissions of the E3Δ–D3Π system are weak. [ABSTRACT FROM AUTHOR]

This study calculates the potential energy curves of 12 Λ-S and 27 Ω states, which belong to the first dissociation channel of SiC + cation. The potential energy curves are computed with the complete active space self–consistent field method, which is followed by the valence internally multireference configuration interaction approach with the Davidson correction. The transition dipole moments are determined. Core-valence correlation and scalar relativistic correction, as well as extrapolation of the potential energies to the complete basis set limit are included. The spin-orbit coupling effect on the spectroscopic parameters and vibrational properties is evaluated. The vibrational band origins, Franck–Condon factors, and Einstein coefficients of spontaneous emissions are calculated. The rotationless radiative lifetimes of the vibrational levels are approximately 10 −5  s long for the e 2 Π state. The partial radiative lifetimes of vibrational levels are approximately 10 −7  s long for the 2 4 Π and 2 4 Σ − states, 10 −5 to 10 −6  s long for the 2 2 Σ − state and the first well of the 1 4 Π state, and very short for the second well of the 1 4 Π state. Overall, the emissions are strong for the 2 2 Σ − –c 2 Σ − , 2 4 Σ − –X 4 Σ − , 2 4 Π–X 4 Σ − transitions, and for the second well of the 1 4 Π–1 4 Σ + transition. The spectral range of emissions is determined. In terms of the radiative lifetimes and transition probabilities obtained in this paper, some guidelines for detecting these states are proposed via spectroscopy. These results can be used to measure the emissions from the SiC + cation, in particular, in interstellar clouds. [ABSTRACT FROM AUTHOR]