| Summary: | Intensity of transitions from the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>b</mi><mn>1</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mi mathvariant="normal">g</mi><mo>+</mo></msubsup><mo> </mo></mrow></semantics></math></inline-formula> and <i>a</i><sup>1</sup>Δ<sub>g</sub> states to the ground state <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi mathvariant="normal">X</mi><mn>3</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mi mathvariant="normal">g</mi><mo>−</mo></msubsup><mo> </mo></mrow></semantics></math></inline-formula> in the near IR emission spectrum of the S<sub>2</sub> molecule has been calculated by the multireference configuration interaction method taking into account spin-orbit coupling (SOC). The intensity of the<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo> </mo><msup><mi>b</mi><mn>1</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mi mathvariant="normal">g</mi><mo>+</mo></msubsup></mrow></semantics></math></inline-formula> − <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mrow><mo> </mo><mi mathvariant="normal">X</mi></mrow></mrow><mn>3</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mrow><mi mathvariant="normal">g</mi><mo>,</mo><mi>M</mi><mi>s</mi><mo>=</mo><mo>±</mo><mn>1</mn></mrow><mo>−</mo></msubsup></mrow></semantics></math></inline-formula> transition is largely determined by the spin interaction with the electromagnetic wave, which comes from the zero-field splitting of the ground X multiplet and the SOC-induced mixing between <i>b</i> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi mathvariant="normal">X</mi><mn>3</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mrow><mi mathvariant="normal">g</mi><mo>,</mo><mn>0</mn></mrow><mo>−</mo></msubsup></mrow></semantics></math></inline-formula> states. The Einstein coefficients for the experimentally detected 0−0, 0−1, 1−1 bands of the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>b</mi><mn>1</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mi mathvariant="normal">g</mi><mo>+</mo></msubsup><mo>−</mo><msup><mi mathvariant="normal">X</mi><mn>3</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mrow><mi mathvariant="normal">g</mi><mo>,</mo><mi>M</mi><mi>s</mi><mo>=</mo><mo>±</mo><mn>1</mn></mrow><mo>−</mo></msubsup></mrow></semantics></math></inline-formula> emission system are calculated in good agreement with observations. The Einstein coefficient of the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>a</mi><mn>1</mn></msup><msub><mo>∆</mo><mi mathvariant="normal">g</mi></msub><mo>−</mo><msup><mi mathvariant="normal">X</mi><mn>3</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mrow><mi mathvariant="normal">g</mi><mo>,</mo><mi>M</mi><mi>s</mi><mo>=</mo><mo>±</mo><mn>1</mn></mrow><mo>−</mo></msubsup></mrow></semantics></math></inline-formula> magnetic dipole transition is very low, being equal to 0.0014 s<sup>−1</sup>. Nonetheless, the weakest of all experimentally observed bands (the 0−0 band of the <i>a-X<sub>Ms=</sub></i><sub>±1</sub> transition) qualitatively corresponds to this calculation. Most importantly, we provide many other IR bands for magnetic dipole <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>b</mi><mn>1</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mi mathvariant="normal">g</mi><mo>+</mo></msubsup></mrow></semantics></math></inline-formula> − <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mrow><mo> </mo><mi mathvariant="normal">X</mi></mrow></mrow><mn>3</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mrow><mi mathvariant="normal">g</mi><mo>,</mo><mi>M</mi><mi>s</mi><mo>=</mo><mo>±</mo><mn>1</mn></mrow><mo>−</mo></msubsup></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>a</mi><mn>1</mn></msup><msub><mo>∆</mo><mi mathvariant="normal">g</mi></msub><mo>−</mo><msup><mi mathvariant="normal">X</mi><mn>3</mn></msup><msubsup><mrow><mstyle mathsize="70%" displaystyle="true"><mo>∑</mo></mstyle></mrow><mrow><mi mathvariant="normal">g</mi><mo>,</mo><mi>M</mi><mi>s</mi><mo>=</mo><mo>±</mo><mn>1</mn></mrow><mo>−</mo></msubsup></mrow></semantics></math></inline-formula> transitions, which could be experimentally observable in the S<sub>2</sub> transparency windows from a theoretical point of view. We hope that these results will contribute to the further experimental exploration of the magnetic infrared bands in the S<sub>2</sub> dimer.
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