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arXiv · 2504.04214

An ab initio spectroscopic model of the molecular oxygen atmospheric and infrared bands

Wilfrid Somogyi·Sergey N. Yurchenko·Gap-Sue Kim
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Abstract

We present a unified variational treatment of the magnetic dipole matrix elements, Einstein coefficients and line strength for general open-shell diatomic molecules in the general purpose diatomic code Duo. Building on previous work in which similar expressions for the electric quadrupole transitions were developed, we also present a complete ab initio spectroscopic model for the infrared, electric dipole-forbidden, spectrum of the $^{16}$O$_2$ molecule. The model covers seven states, namely the X $^3\Sigma^-_g$, a $^1\Delta_g$, b $^1\Sigma^+_g$, I $^1\Pi_g$, II $^1\Pi_g$, I $^3\Pi_g$ and II $^3\Pi_g$ states, for which 7 potential energy, 6 electronic angular momentum, 7 spin-orbit, and 14 quadrupole moment curves are calculated using ic-MRCI theory and an aug-cc-pV5Z basis set. These curves are diabatised to remove avoided crossings between the excited $\Pi$ states, and the resultant properties are used to produce a line list for higher-order transitions of astrophysical interest.

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Wilfrid Somogyi, Sergey N. Yurchenko, Gap-Sue Kim. 2025-04-05. An ab initio spectroscopic model of the molecular oxygen atmospheric and infrared bands. https://doi.org/10.1039/d4cp02619e

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