Schedule Mar 15, 2013
Photostop: Towards Magnetic Trapping of Cold SH/SD Radicals Produced by Photodissociation
Eckart Wrede (Durham Univ.)

L. Deng1, D. Carty1,2 and E. Wrede1

Joint Quantum Centre (JQC) Durham-Newcastle
 Department of Chemistry, Durham University, U.K.

2 Department of Physics, Durham University, U.K. 

We have demonstrated that photofragments can be produced at rest in the laboratory frame after the photodissociation of a precursor molecule--a technique we call photostop. If the recoil speed of the photodissociation event is matched to the speed of the precursor molecules in a supersonic molecular beam those photofragments that recoil opposite to the precursor velocity will be created at zero velocity in the laboratory frame. Molecular and atomic fragments (NO from NO2 dissociation [1] and Br from Br2 dissociation [2]) have been successfully stopped and their free evaporation from the probe volume monitored via resonance-enhanced multi-photon ionization for up to 10 and 100 ?s after the dissociation, respectively.

We will present our latest data of cold SH and SD radicals produced with the photostop technique inside a static magnetic trap and our recent efforts to enhance the detection limit for laser-induced fluorescence in order to detect magnetically trapped SD radicals. We will compare our experimental data to simulations of the photodissociation and evaporation processes in free space and within the trap and discuss the prospect of the accumulation of molecules created by subsequent laser pulses.

We are currently designing a new apparatus that will incorporate multiple detection techniques to achieve absolute density measurements inside the trap: cavity ring-down spectroscopy combined with laser-induced fluorescence and resonance-enhanced multi-photon ionisation. 

[1]A. Trottier, E. Wrede and D. Carty, Mol. Phys. 109, 725 (2011).

[2]W.G. Doherty, M.T. Bell, T.P. Softley, A.M. Rowland, E. Wrede and D. Carty, PCCP 13, 8441 (2011).

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