Metastable rovibrational f-symmetry levels of the I ¹Π_g state of H₂, HD and D₂: experiment and theory

Abstract

We present accurate experimental measurements of the lifetimes and term values of the metastable rovibrational f-symmetry levels of the I ¹Π_g state of HD. These levels lie above the second dissociation limit of hydrogen. The lifetimes were obtained directly from the observation of the time-dependent decay of the fluorescence. These levels decay by direct fluorescence and by predissociation after tunnelling through the potential energy barrier of the I ¹Π_g state. We present ab initio results for both of these decay processes for H₂, HD and D₂. The theoretical calculations provide an explanation of the rotational dependence of the observed lifetimes for HD, the lack of rotational dependence for D₂, and the approximately equal lifetimes for N = 1 for HD and D₂. The calculated lifetimes for the metastable levels of H₂ explain why no experimental data is yet available for the parent isotopomer. However, the use of recently updated Hönl–London factors with published ab initio electronic transition moments reveals a larger than expected discrepancy with experiment for those levels of HD and D₂ for which emission is the dominant decay mechanism.

Keywords:

• I ¹Π_g state
• Hydrogen molecule
• Experimental fluorescence lifetimes
• Tunnelling predissociation
• Ab initio lifetimes

Notes

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Additional information

Notes on contributors

Koichi Tsukiyama∥

∥[email protected]