Transition Probabilities of Emissions and Rotationless Radiative Lifetimes of Vibrational Levels for the SiN Radical

Abstract

Abstract The transition dipole moments of the SiN radical are calculated by the valence internally contracted multireference configuration interaction (icMRCI) approach with the aug-cc-pV6Z basis set. The transition probabilities of spontaneous emissions are computed between the eight lowest-lying doublet states. The vibrational band origins, Einstein coefficients, and Franck–Condon factors of all the spontaneous emissions involved are evaluated. The rotationless radiative lifetimes of the first 15 vibrational levels were determined to be approximately 10−3–10−5 s long for the A2Π state, 10−3–10−7 s long for the F2Π state, 10−6–10−7 s long for the C2Π state, 10−6 s long for the D2Σ− and E2Δ states, and 10−7 s long for the B2Σ+ and G2Δ states. It is observed that the rotationless radiative lifetimes quickly become shorter, with an increase in the vibrational level for the A2Π and F2Π states. The Einstein coefficients of many emissions are large for the B2Σ+–X2Σ+, B2Σ+–A2Π, C2Π–X2Σ+, C2Π–A2Π, D2Σ−–A2Π, E2Δ–A2Π, F2Π–X2Σ+, F2Π–A2Π, and G2Δ–A2Π systems. However, the emissions are very weak for the F2Π–D2Σ− system. The vibrational levels and rotational constants of each state are determined and the spectral range of each transition system is evaluated. The vibrational band origins are compared with the available experimental ones. The spectroscopic routines for detecting the unobserved states are proposed. These results can be employed to measure emissions, in particular those of interstellar clouds and stellar atmospheres.