Spectra of dipole bound states and their role in the electron attachment in interstellar clouds Felix Güthe 1,2 1 abcd Switzerland Ltd., Baden, Switzerland 2 Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland Royal Astronomical Society meeting "Polyatomics and DIBs in Diffuse Interstellar Clouds" on 8 and 9 Jan at UMIST. Thanks to : John Maier Marek Tulej M. V. Pachkov Thomas Pino

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Spectroscopic techniques Spectral range: UV/visible for DIBs Direct absorption –I/I 0 –sensitivity and selectivity –multiple passes and Cavity Ring Down Spectroscopy or Laser induced Fluorescence excited state lifetime, fluorescence quantum yield Mass selective techniques –Resonance Enhanced Multi Photon Ionisation (and related - R2ColourPhotoDetachment) –change in the m/z ratio (anion  neutral ; neutral  cation, cation  Fragment) –sensitivity for ion detection is high! –additional molecular information: mass –physics of the ionisation/detachment process is important

Experimental setup resonant two colour photo detachment R2CPD

Massspectrum of the ion source

Anion spectroscopy A    A +e - Photodetachment threshold

Dipole bound states -DBSs analogous to Rydberg states for neutrals - large orbital requires a minimum dipole moment of ~ Debye to bind extra electron ground state or excited state rovibrationally excited states of the DBS can be unbound M. Gutowski et al.

PD-Spectra of C 2n H - (n=2-4) 1   1  + transitions close to the threshold (EA). binding energies ~ cm -1 for C 4 H - DBS connected to an excited neutral state (E( 2 )> E( 2  + )) transitions in the UV (no DIBs) (<350nm)

Origin of C 4 H - (DBS) rotational resolution, bent upper state

PD-spectrum of l-C 3 H 2 - (DBS) assigned by: K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, , 1996

PD-spectrum with different excitation / detachment lasers Molecular beam T= ~50K bound states only visible in upper traces

K-structure of the two strongest vibronic bands

Comparison to DIBs

LaboratoryAstronomical Peak nmDIB (nm)fwhm (nm) EW (mÅ) A (7)699.32(J) (G) A (7)678.87(J) (W)2.3 A (1)649.19(J) (W) (T) A (2)615,115(T) B (30)496.40(J) (T) (K) C (15)498.47(J) ,478(T) (K) C (30)488,18(J) ,04(J) (T)1.49>466 J=Jenniskens & Desert (1994), G=Galazutdinov et al. T= Tuairisg et al. (2000), W = Weselak et al. (2000) All bands in question are narrow only the origin band is considered strong

full PD-Spectrum of l-C 3 H 2 -

Ratio of anions to neutrals k att = electron attachment k col = collisional detachment k det = photodetachment k rec = recombinational detachment Anion abundance in diffuse interstellar clouds k f = formation rate temporary negative ion (~r -2 ) k r = radiative stabilisation ( s -1 ) k DA = dissociative association k AD = autodetachment

Anion abundance in diffuse interstellar clouds The capture probablity (k f ) of slow electrons by polar neutrals is high Attachment will be enhanced by rovibrational Feshbach states (“doorway states”) for fast internal conversion (IC) to the electronic ground state radiative stabilisation (k r ) can compete with autodetachment (k AD ) for slow IC the lifetime of the resonance has to be sufficiently long to compete with k AD

Conclusions DIB for l-C 3 H 2 - match not unlikely or disproven. Anion formation is possible for polar molecules with high EA (as detected by MW spectroscopy) DBS transitions are strong and in the vis /near UV Intensity would be only 0.5 % of all DIBs and No. 45 (in intensity) in Jennikens compilation the most intense DIBs are propably not DBS

Lifetime of rovibrational Feshbach states 400 cm -1 above the binding energy AD could not be observed at the threshold AD lifetimes must be longer than radiative stbilisation (k r ) K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, , 1996

Comparison to Yokohama et al. R2CPD 50 K our work K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, , 1996 one colour high resolution 500K

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, , H 2 CCC – :discrepancy between two experiments

let’s compare this: p overlapping the upper and the lower graph with our data ->

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, , H 2 CCC – : upper graph: ok, bu t than the frequency and the origin position in Yokoyama et al. disagree

K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, , H 2 CCC – :discrepancy between two experiments ?? lower graph

H 2 CCC – :origin K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, , 1996.

H 2 CCC – :discrepancy between two experiments K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, , at cm -1 freq. cited Iodine calibration * = estimation laboratory bandDIB (best value)coinc.? (7) (1.5) (J)+ (s) (7) (1.5) (J)? (1) (0.3) (W)+ (w) (2) (0.5) (T)?

conclusion about coincidence discrepancies: –our lab -DIB <1cm -1 –our lab -simulation Yokoyama <1cm -1 –precision of our laser (no iodine) ~1cm -1 –our spectrum overlaps with DIB –the position of the DIB has not changed from Jenniskens to McCall or Galazutdimov the two spectra from p don’t agree O° is perturbed (p paragraph B) O° is not visible in Yokoyama -> How can McCall / Oka rule out the Match ?

PD-spectrum of l-C 3 H 2 - and l-C 3 D 2 - (DBS)

Levels of the K-structure coldest transition belongs to the 0-1 K- stack B. J. McCall, T. Oka, J. Thorburn, L. M. Hobbs, and D. G. York The Astrophysical Journal, 567:L145–L148, 2002

2002 study on l-C 3 H 2 - Bands B. J. McCall, T. Oka, J. Thorburn, L. M. Hobbs, and D. G. York The Astrophysical Journal, 567:L145–L148, 2002

PD-spectrum of l-C 3 H 2 - and l-C 3 D 2 - ( Feshbach states )

end C3H2- additional material

Autodetaching states of C 3 - EA = 1.995eV

Origin band A 2  u -X 2  g Rotational profiles of the band origins Origin band B 2  u - -X 2  g life time  < 5ps

Autodetaching states of C 3 -

R2CPD spectra of the C N H - (odd)

R2CPD and Matrix spectra of C 2n H -

Two isomers of C N H - structured band for (c) only in gas phase! intensities can be differed in matrix!

Orgins of the C N H - anions DIB-range

MH - + e- MH - +h vis M - + H MH *- (TNI)  (e-), T,  (e-) f, ISRF, EA k 2,[H,H 2 ] MH -* MH - +h vis M - + H MH + e- MH - +h IR k ISC k AD k AD,vib k rad,IR k rad,vis k DA k DA,RRKM ?? Kinetics of the Anion Chemistry not included: high energetic radition, shocks, dust grain chemistry

Gasphase R2CPD spectrum of C 7 - Laboratory Astronomical

Comparison with astronomical data 1st vibronic band origin band astronomy laboratory 

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end anions additional material