Emission from an NO
2− ion in KBr is studied under resonant excitation with laser light at vibration-rotation structures of the
1A
1→
1B
2 transition. Five rotational Raman lines are identified in a fundamental and over-tone vibrational transitions with Raman shift energies of +4.4, 0, −4.4, −10.0 and −14.5 cm
−1 from the vibrational transitions. A new assignment for the rotational structures in the absorption, emission and Raman spectra is proposed, which is based on a one-dimensional rotor in a hindering potential with four-fold symmetry. The rotational constants and hindering potentials are determined as
A=1.3 cm
−1,
V⁄
A=4 and
A′=1.7 cm
−1,
V′⁄
A′=8 for the ground and excited electronic state, respectively. These values suggest that the rotation occurs around an axis passing near an N-atom and perpendicular to the symmetry axis in the molecular plane.
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