Experiments on NO
2 reveal a substructure underlying the optically excited isolated hyperfine structure (hfs) levels of the molecule. This substructure is seen in a change of the symmetry of the excited molecule and is represented by the two “states”
and
of a hfs-level. Optical excitation induces a transition from the ground state
of the molecule to the excited state . However, the molecule evolves from
to
in a time
τ0 ≈ 3
μs. Both
and
have the radiative lifetime
τR ≈ 40
μs, but
and
differ in the degree of polarization of the fluorescence light. Zeeman coherence in the magnetic sublevels is conserved in the transition
→, and optical coherence of
and
is able to affect (inversion effect) the transition
→. This substructure, which is not caused by collisions with baryonic matter or by intramolecular dynamics in the molecule, contradicts our knowledge on an isolated hfs-level. We describe the experimental results using the assumption of extra dimensions with a compactification space of the size of the molecule, in which dark matter affects the nuclei by gravity. In
, all nuclei of NO
2 are confined in a single compactification space, and in
, the two O nuclei of NO
2 are in two different compactification spaces. Whereas
and
represent stable configurations of the nuclei,
represents an unstable configuration because the vibrational motion in
shifts one of the two O nuclei periodically off the common compactification space, enabling dark matter interaction to stimulate the transition
→ with the rate (
τ0)
−1. We revisit experimental results, which were not understood before, and we give a consistent description of these results based on the above assumption.