Quantum-interference effects in the o ¹Π_u(v=1)∼b¹Π_u(v=9) Rydberg–valence complex of molecular nitrogen

Abstract

Two distinct high-resolution experimental techniques, 1 UV laser-based ionization spectroscopy and synchrotron-based XUV photoabsorption spectroscopy, have been used to study the o Rydberg–valence complex of ¹⁴N₂, providing new and detailed information on the perturbed rotational structures, oscillator strengths, and predissociation linewidths. Ionization spectra probing the b state of ¹⁴N₂, which crosses o¹Π_u(v=1) between J = 24 and J = 25, and the o¹Π_u(v=1), b,¹Π_u(v=9), and b states of ¹⁴N¹⁵N, have also been recorded. In the case of ¹⁴N₂, rotational and deperturbation analyses correct previous misassignments for the low-J levels of o(v=1) and b(v=9). In addition, a two-level quantum-mechanical interference effect has been found between the o–X(1, 0) and b–X(9, 0) transition amplitudes which is totally destructive for the lower-energy levels just above the level crossing, making it impossible to observe transitions to b(v=9,J=6). A similar interference effect is found to affect the o(v=1) and b(v=9) predissociation linewidths, but, in this case, a small non-interfering component of the b(v=9) linewidth is indicated, attributed to an additional spin–orbit predissociation by the repulsive state.

Keywords:

• Predissociation
• Perturbation
• Diatomic molecules
• Extreme ultraviolet
• Laser spectroscopy

Acknowledgements

The authors gratefully acknowledge the support provided for this research by the following bodies: the Molecular Atmospheric Physics (MAP) Program of the Netherlands Foundation for Fundamental Research on Matter (FOM); the Australian Research Council's Discovery Program (project number DP0558962); and NASA (grant NNG05GA03G). The assistance of the staff of the Photon Factory is also acknowledged.