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Production of Molecular Ions Using a Hollow-Cathode Spectrometer Trevor Cross, Nadine Wehres, Mary Radhuber, Anne Carroll, Susanna Widicus Weaver Department.

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Presentation on theme: "Production of Molecular Ions Using a Hollow-Cathode Spectrometer Trevor Cross, Nadine Wehres, Mary Radhuber, Anne Carroll, Susanna Widicus Weaver Department."— Presentation transcript:

1 Production of Molecular Ions Using a Hollow-Cathode Spectrometer Trevor Cross, Nadine Wehres, Mary Radhuber, Anne Carroll, Susanna Widicus Weaver Department of Chemistry, Emory University, Atlanta, GA, USA

2 Motivation for Laboratory Search of Ions in ISM Tracers of chemical and physical conditions in ISM (Herbst & van Dishoeck 2009) Important intermediates in chemical networks New telescopes coming online

3 Why a Hollow Cathode? Efficient creation of protonated species (Gabrys 1995) Long pathlength Access to highly excited species

4 Schematic Detector Lock-in Amplifier Synthesizer N2H+N2H+ To PumpSample Input LN 2 Cooling Recirculating Chiller HV THz Source Lens Design based on Amano Design based on Gabrys et al. J. Phys. Chem. 99 (42)(1995)

5 Further Specifications Copper cell with cooling coils Stainless Steel anode with cooling lines Liquid nitrogen, water or ethylene glycol cooling Pressure: 50 mTorr of sample gas in argon Tunable HV power supply (max V), (typical instrument settings: V and 180 mA)

6 Target Molecules N 2 H + for benchmark and proof of concept N 2 D + up to 1 THz H 5 + isotopologues

7 Background of Target molecules N 2 H + and N 2 D + N 2 H + first observed in the ISM. (Turner 1974) First experimental detection of both N 2 D + and N 2 H + (Saykally 1976) N 2 H + fully characterized up to 2 THz (Amano 2005, refs. therein) N 2 D + characterized up to J’-J”=9-8 at 700 GHz Important tracers (Herbst 1989, Loren 1995, Lepp 1984)

8 N 2 H + Detections Detected N 2 H + transitions between 300 GHz up to 1 THz Conditions for experiment 5 sccm H 2, 5 sccm N 2, 40 sccm Ar Proof of concept for experiment

9 N 2 H + Detections

10 N 2 D + Detections N 2 D + detected in the range of 300 GHz to 1 THz. Same conditions as N 2 H + Higher frequency transitions were calculated by JPL/CDMS Confirmation of predicted transitions between GHz J’-J” = 10-9 through J’-J” = 13-12

11 CDMS JPL N2D + Detections

12 Significance of N 2 D + Detections Observers can unambiguously identify these new N 2 D + lines relying on experimental detections. Significant difference from predictions Refined molecular constants

13 New Molecular Constants and Fit TransitionsObservedCalculatedJPLCDMS (40) (1.2) (32) (40) (1.6) (44) (40) (2.2) (60) (40) (2.8) (78) ParametersThis WorkDore et al 2004 B (MHz) (90) (26) D (kHz) (46)61.552(47) eQq (13) (42) eQq (24) (73) C(N 1 )3.87(18) x (84) x C(N 2 )5.57(24) x (11) x 10- 3

14 Future and Work in progress H 2 D + and D 2 H + available from the CDMS and JPL databases H 5 + isotopologues measurements Other weakly bound ions or radicals

15 H 5 + Isotopologues Highly fluxional and weakly bound cluster Molecular interaction Three isotopologues with dipole moments: H 3 D 2 +, H 2 D 3 +, and H 4 D + McGuire et al. 2011

16 H 5 + Isotopologues Boltzmann Peak Warmer excited states more accessible Ideal peak for spectral range McGuire et al K 300K

17 Acknowledgements This work is supported by NSF CAREER Award CHE Thanks to the Widicus Weaver group


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