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The role of asymptotic states in H 3 + Jonathan Tennyson Department of Physics and Astronomy Royal Society University College London Jan 2006 HPCx supercomputer: Daresbury Laboratory

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Spectroscopy of H 3 + “Solved problem” at low energy How about near dissociation? Nature of (rotation-)vibration states? Radiative association: H 2 + H + H 3 + + h Isotope exchange eg HD + H 3 + H 2 + H 2 D + Meilke et al, Phys. Rev. Lett. 91, 063201 (2003)

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Accurate H 3 + PES Realistic potential energy surface: Polyansky et al, Mol. Phys., 98, 261 (2000). r R Jacobi coordinates

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Density of states: requires serious computer power Even states

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H 3 + near dissociation vibrational state

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Calculated rotational constants for H 3 + JJ Munro, J Ramanlal & J Tennyson, New J Phys, 7, 196 (2005)

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r R =90 Classical trajectory at 19600 cm -1

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Poincare surface of section at 19600 cm -1 r p

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Classical trajectory above dissociation r R =90 “Feshbach” resonance

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Poincare surface of section for D 0 > E > D e

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Creates H 3 + Detects H + CO 2 laser: 800 – 1000 cm -1 H 3 + + h H 2 + H + Near-dissociation photodissociation experiment of Carrington et al

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Quantum states at dissociation: Near dissociation spectrum of H 3 + by Carrington et al 25000+ discrete lines in 222 cm -1

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Technique for characterising resonances 1.Solve H 0 0 = E 0 for all E including > D 0. 2.Solve H = H 0 + i U(R) for 0 dropping bound solutions; i U(R) is complex absorbing potential (CAP). 3. Vary to identify resonances in complex plane.

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Continuum wavefunction r R = 90

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Complex Absorbing Potential (CAP) comparison

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Position Width Locating resonances using a CAP

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Vibrational (Feshbach) resonances Width ( ) > 1 cm -1 Too short lived to be important for photodissociation spectrum

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Shape resonances: rotational states trapped by centrifugal barrier KE release

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Complete model of H 3 + near-dissociation photodissocation spectrum Vibrational states @ dissociation + above Rotational states @ dissociation + above Resonances: lifetime effects Dipole transitions: spectroscopy Asymptotic Vibrational States (AVS) Robust Present in other (all?) molecules eg O 3, NO 2

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Bruno Silva Paolo Barletta James Munro ChemReact High Performance Computing Consortium

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