Triplet excited states of the N2 molecule play an important role in electric discharges through air or liquid nitrogen accompanied by various afterglows. In the rarefied upper atmosphere, they produce aurora borealis and participate in other energy-transfer processes connected with atmospheric photochemistry and nightglow. In this work, we present spin–orbit coupling calculations of the intensity of various forbidden transitions, including the prediction of the electric dipole transition moment of the new 13Σg−← A3Σu+ band, which is strongly prohibited by the (+|−) selection rule, the new spin-induced magnetic B′3Σu−← A3Σu+ transition, magnetic and electric quadrupole transitions for the B3Πg← X1Σg+ Wilkinson band, and the Lyman–Birge–Hopfield a1Πg ← X1Σg transition. Also, two other far-UV singlet–singlet quadrupole transitions are calculated for the first time, namely, the Dressler–Lutz a"1Σg+–X1Σg+ and the less studied z1Δg–X1Σg+ weak transitions.
Density functional theory calculations for p-Br-N-sulfinylaniline and m-nitro-N-sulfinylaniline in the ground singlet (S0) and triplet (T1) excited states are presented and analyzed in terms of their specific physicochemical properties. As all aromatic N-sulfinylamines, these compounds are rather unstable being sensitive to moist air and we assign this instability to the thermally allowed S0T1 excitation induced by internal magnetic forces. Our calculations indicate that the T1–S0 energy gap in these molecules is unexpectedly low and spin-orbit coupling matrix element between these states is relatively high, being allowed by the orbital symmetry selection rules. We also apply the exchange mechanism of spin-catalysis concept in order to explain the prone of N-sulfinylamines to the Diels-Alder cycloaddition with dienes.
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