Dresden 2011 – scientific programme

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MO: Fachverband Molekülphysik

MO 19: Cold Molecules III

MO 19.1: Talk

Wednesday, March 16, 2011, 16:30–16:45, BAR Schön

Visible rovibrational spectroscopy of cold H₃⁺ via chemical probing in a 22 pole trap — •Florian Grussie, Max Berg, Andreas Wolf, and Annemieke Petrignani — Max-Planck Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg

H₃⁺ is the cornerstone of interstellar chemistry and the simplest triatomic molecule, therefore also of fundamental interest to experimental and theoretical physics. At the MPI for Nuclear Physics, spectroscopy on cold H₃⁺ is performed in a cryogenic 22-pole radiofrequency trap using laser-induced reactions with argon as chemical probe. The chemical probing technique provides high sensitivity and a low background environment, so that transitions up to at least 6 orders of magnitude weaker than the fundamental (B₂₁=4.77 · 10²³ cm⁻³J⁻¹s⁻¹) can be observed. This high sensitivity is augmented by an efficient Daly detection system where each ion is amplified into a bunch of secondary electrons that are subsequently amplified into photons before being counted by a photomultiplier tube. This has allowed us to measure transitions from the two lowest rotational states of the H₃⁺ vibrational ground state to, recently, final levels up to 16600 cm⁻¹, i.e., half the dissociation energy. To observe transitions to even higher levels, the already low background needs to be minimized further. The background originates from non-laser-induced probe ions and laser photons. The latter should be eliminated by a new detection system insensitive to our laser photons. The non-laser-induced ions can be minimized by injecting the argon chemical probing gas during laser excitation only, using a pulsed valve.