Laboratory Astrophysics: Or, Finding an Anion in a Haystack Part I: Tutorial

Transcription

1 Laboratory Astrophysics: Or, Finding an Anion in a Haystack Part I: Tutorial Sandra Brünken I. Physikalisches Institut, Universität zu Köln, Germany Workshop Negative ions and molecules in astrophysics August , Gothenburg

2 Overview Introduction The Molecular Universe Reminder: Molecular Complexity Experimental Methods and Examples: General Approach Terahertz Absorption Spectrometer Fourier Transform Microwave Spectrometer Spectroscopy in Ion Traps Summary

3 The Cosmic Cycle in Molecules cold dark clouds: unsaturated, radicals long carbon chains warm star forming regions: complex organic molecules, e.g., CH 3 CO, C 2 H 5 CO, CH 3 OCH 3,. H 2, CO, CH, CN, CH +, C 2, C 3, HCN,. dust Bill Saxton, NRAO/AUI/NSF

4 Dense Interstellar Cloud Cores T 10 K n cm -3 sites of star formation H 2 dominant Molecules seen in IR absorption and radio emission Cosmic rays create weak plasma Fractional ionization < 10-7

5 Warm (Hot) Molecular Cores T > 100 K n > 10 7 cm -3 saturated, complex molecules Herschel/HIFI Spectrum of Water and Organics in the Orion Nebula

6 The Cosmic Cycle in Molecules H 2, CO, CH, CN, CH +, C 2, C 3, HCN,. dust cold dark clouds: unsaturated, radicals long carbon chains warm star forming regions: complex organic molecules, e.g., CH 3 CO, C 2 H 5 CO, CH 3 OCH 3,. Circumstellar shells NaCl, AlC, AlF, SiC, SiC4, carbon chains Bill Saxton, NRAO/AUI/NSF

7 Circumstellar Envelopes IRC IRC Guélin et al. (1997) Izan Leao (2006), ESO / VLT 100 Ziurys (2006)

8 The Cosmic Cycle in Molecules H 2, CO, CH, CN, CH +, C 2, C 3, HCN,. dust cold dark clouds: unsaturated, radicals long carbon chains Molecules: probe and influence physical conditions chemical inventory and formation processes warm star forming regions: complex organic molecules, e.g., CH 3 CO, C 2 H 5 CO, CH 3 OCH 3,. Circumstellar shells NaCl, AlC, AlF, SiC, SiC4, carbon chains Bill Saxton, NRAO/AUI/NSF

9 Astrochemistry Astrophysical Observation Laboratory Astrophysics Chemical Modells of Interstellar Objects Chris Madden

10 Molecules in the ISM - Laboratory Astrophysics Formation & destruction processes: Gas phase chemical kinetics & reaction dynamics Photochemistry Ice chemistry, dust surface reactions & gas - grain interactions Excitation mechanisms: Collisional rates & radiative (de-) excitation Identification & quantification: Rotational, vibrational & electronic spectroscopy Transition moments

11 Molecules detected in the ISM and CSM (cdms 8/11) 2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms 8 atoms 9 atoms H 2 C 3 * c-c 3 H C 5 * C 5 H C 6 H CH 3 C 3 N CH 3 C 4 H AlF C 2 H l-c 3 H C 4 H l-h 2 C 4 CH 2 CHCN HC(O)OCH 3 CH 3 CH 2 CN AlCl C 2 O C 3 N C 4 Si C 2 H 4 * CH 3 C 2 H CH 3 COOH (CH 3 ) 2 O C 2 ** C 2 S C 3 O l-c 3 H 2 CH 3 CN HC 5 N C 7 H CH 3 CH 2 OH CH CH 2 C 3 S c-c 3 H 2 CH 3 NC CH 3 CHO H 2 C 6 HC 7 N CH + HCN C 2 H 2 * H 2 CCN CH 3 OH CH 3 NH 2 CH 2 OHCHO C 8 H CN HCO NH 3 CH 4 * CH 3 SH c-c 2 H 4 O l-hc 6 H* CH 3 C(O)NH 2 CO HCO + HCCN HC 3 N HC 3 NH + H 2 CCHOH CH 2 CHCHO? C 8 H CO + HCS + HCNH + HC 2 NC HC 2 CHO C 6 H CH 2 CCHCN C 3 H 6 CP HOC + HNCO HCOOH NH 2 CHO H 2 NCH 2 CN SiC H 2 O HNCS H 2 CNH C 5 N HCl H 2 S HOCO + H 2 C 2 O l-hc 4 H* KCl HNC H 2 CO H 2 NCN l-hc 4 N NH HNO H 2 CN HNC 3 c-h 2 C 3 O NO MgCN H 2 CS SiH 4 * H 2 CCNH? NS MgNC H 3 O + H 2 COH + C 5 N NaCl N 2 H + c-sic 3 C 4 H OH N 2 O CH 3 * HC(O)CN PN NaCN C 3 N SO OCS PH 3? SO + SO 2 HCNO SiN c-sic 2 HOCN SiO CO 2 * HSCN SiS NH 2 H 2 O 2 CS H 3+ * HF H 2 D + +, HD 2 HD SiCN FeO? AlNC O 2 SiNC CF + HCP SiH? CCP PO AlOH AlO H 2 O + OH + H 2 Cl + CN KCN SH + FeCN CH CH CN + A Molecular Universe H 2O NH 3 OH Year 10 atoms 11 atoms 12 atoms >12 atoms CH 3 C 5 N HC 9 N C 6 H 6 * HC 11 N (CH 3 ) 2 CO CH 3 C 6 H C 2 H 5 OCH 3? C 60 * (CH 2 OH) 2 C 2 H 5 OCHO n-c 3 H 7 CN C 70 * CH 3 CH 2 CHO Total: positive ions 6 negative ions

12 intensity Identifying molecules in space radiation source absorption cell detector = frequency Astronomical needs: transition frequencies to an accuracy of Dn/n = 10-6 background source interstellar cloud circumstellar shell radio telescope

13 Levels of Complexity 2B CO diatomic closed shell rigid

14 Levels of Complexity H 2 CO m a asymmetric top closed shell rigid

15 Levels of Complexity CH 2 asymmetric top light & floppy m b radical 3 B 2 spin-orbit interaction + hfs

16 Levels of Complexity CH 3 OH asymmetric top a- and b-type closed shell internal rotor

17 The spectroscopist s To Do list Quantum chemical ab initio calculations to get an idea of the structure and rotational spectrum Finding an efficient way to produce the molecule High resolution measurements over a broad range of the spectrum Understand your molecule : Fitting the observed lines to an effective rotational Hamiltonian to predict its full spectrum and intensities

18 Laboratory absorption spectroscopy tunable, monochromatic radiation source absorption cell broadband detector backward wave oscillator synthesizer, Gunn diodes solid state multiplier chains (up-conversion) photomixing (down-conversion) FIR laser (sideband) systems Quantum Cascade Lasers VDI 1.9 THz multiplier chain GREAT / SOFIA

19 Laboratory absorption spectroscopy tunable, monochromatic radiation source absorption cell broadband detector stable (bottled) gases discharges: RF, DC, AC pyrolysis supersonic jets laser ablation Radicals: CH 2, C 2 H, CN,... Ions: H 3+, CO +, C 6 H -, OH - Isomers: HNC, HOCN,... Refractory Species: TiO 2, organics,...

20 Laboratory absorption spectroscopy tunable, monochromatic radiation source absorption cell broadband detector hot electron bolometer (HEB) Schottky diodes Ge:Ga photoconductors InSb HEB QMC Instruments Ltd.

21 Cologne Superlattice Spectrometer for THz PC Synthesizer Synthesizer 2F Modulation Lock-In 350 MHz 16 GHz PLL IF Harmonic Mixer ~250 GHz SL Lens Lens Absorption cell THz Bolometer Power Supply High Accuracy / High Frequency / High Sensitivity / Broad Band Coverage

22 Cologne Superlattice Spectrometer for THz ND 2 H 70 periods 14 monolayer GaAs 3 monolayer AlAs D 2 O C. P. Endres, F. Lewen, T. F. Giesen, S. Schlemmer, D. G. Paveliev et al. Rev. Scientific Instr. (2007)

23 Example Dimethyl Ether (DME) Broadband Tunability EE J Ka Kc = EA AE AA

24 Rotational Transitions of DME in Ground and First Excited State Intensity [a.u.] ALMA HERSCHEL SOFIA Dimethyl Ether Spectrum at 150 K m b = 1.3 D Pasadena JPL Cologne Frequency [THz] Columbus FASSST ( GHz) Endres PhD thesis

25 Detection of vibrationally excited DME with APEX G high-mass star forming region narrow line widths Minier et al., Astronom. Astrophys., 501 L1 (2009) Priv. Comm. S. Jørgensen- Bisschop

26 Production of ions discharge cells use of DC discharge cells for the production of ions Silvia Spezzano, Cologne T. Oka s Black Widow

27 Jet Spectrometer Fourier Transform Microwave (FTMW) supersonic nozzle coupled to a high-q Fabry-Perot cavity discharge nozzle Q ~ 40,000 movable mirror 1 msec or: pulsed laser ablation source FFT FID ~100 msec cooled to 77 K frequency range: 5 42 GHz resolution: 20 khz accuracy: 1-2 khz production of transient species in discharges of precursor diluted in Ne (He, H 2 ) rotationally COLD molecules (T = 2 K)

28 FTMW Example: HSCN HNCS HSCN HCNS isothiocyanic acid thiocyanic acid thiofulminic acid pulsed discharge of H 2 S (0.2 %) and (CN) 2 (0.2 %) or CH 3 CN (0.2 %) in Ne Brünken et al., ApJ 2009

29 HSCN Astronomical Detection in Sgr B2 (N) ARO 12m telescope Kitt Peak detection of 8 rotational transition in Sgr B2 (N) 2 rotational transitions in TMC-1 Halfen et al., ApJ 2009 Adande et al., ApJ 2010

30 Spectroscopy in electrodynamic ion traps Cryogenic 22-pole ion trap Mass selected Ions Number of Ions Temperature ions Density cm -3 O. Asvany, S. Schlemmer et al., Rev. Sci. Instrum. 81, K (2010) Reaction Rates cm 3 s - 1

31 Deuterated molecules in the interstellar medium deuterated H 3+ as probe for cold, depleted prestellar cores deuterium enrichment H 2 D GHz cosmic [D]/[H] ~ deuterium reservoir [HD]/[H 2 ] ~ D 2 H GHz Isotope enrichment [AD]/[AH] ~ 0.1 M17 SW H 3+ + HD H 2 D + + H K Ground state transitions: H 2 D THz D 2 H THz B. Parise, A. Belloche, F. Du, R. Güsten and K. Menten A&A 526, A31 (2011)

32 Primary Deuteration Reactions E Reactants Products DE H 3+ + HD H 2 D + + H K H 3 + H 2 D +

33 Laser Induced Reactions probing H 2 D + H HD H 2 D + + H K K X 0 0 Reaction 1 01 THz p-h 3 + o-h 3 + p-h 2 D + o-h 2 D +

34 Laser Induced Reactions probing H 2 D + H 2 D + APEX SOFIA Other Ions: anions?! O. Asvany et al., PRL 100, (2008) Δ = 62 MHz (!)

35 Summary High resolution spectroscopy a prerequisite for astronomical observations Active area of research:» Extension of frequency range» Identifying new molecular species» Developing sensitive detection schemes Stay tuned for the anion detection success story!