1+1′ resonant multiphoton ionisation of OH radicals via the A²Σ⁺ state: insights from direct comparison with A-X laser-induced fluorescence detection

^†Invited contribution based on the Molecular Physics Lecture at the Dijon 2011 High Resolution Molecular Spectroscopy Conference.

Abstract

A 1+1′ resonance-enhanced multiphoton ionisation (REMPI) scheme for OH X²Π radicals is characterised for a broad range of intermediate A²Σ⁺ (v = 1, J, F_i) levels. The intensities of OH A-X (1,0) transitions detected by subsequent fixed-frequency VUV ionisation are compared with those obtained by near simultaneous laser-induced fluorescence (LIF) measurements. The ratios of the 1+1′ REMPI to LIF signals are used to derive enhancement factors which reflect the VUV absorption to the OH A³Π, 3d, v = 0 Rydberg state and/or the fast autoionisation process that yields OH⁺ ions. The determination of the enhancement factors permits 1+1′ REMPI to be utilised as a quantitative state-specific probe of OH X²Π radicals.

Keywords:

• OH
• REMPI
• laser-induced fluorescence

Acknowledgements

The authors thank Craig Murray and Robert W. Field for helpful discussions.

Supplemental data

Supplemental data for this article can be accessed here.

Notes

^† Invited contribution based on the Molecular Physics Lecture at the Dijon 2011 High Resolution Molecular Spectroscopy Conference.

The polarization of the 118 nm light may not be well defined after passing through the MgF₂ lens.

Additional information

Funding

This research was supported by the U.S. Department of Energy, Basic Energy Sciences [grant number DE-FG02-87ER13792].