Spectra of dipole bound states and their role in the electron attachment in interstellar clouds Felix Güthe 1,2 1 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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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.
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Spectra of dipole bound states and their role in the electron
attachment in interstellar clouds
Felix Güthe1,2
1 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 MaierMarek Tulej
M. V. PachkovThomas Pino
taken from:http://cfa-www.harvard.edu/cfa/mmw/mmwlab/ismmolecules_organic.html
Spectroscopic techniques
Spectral range: UV/visible for DIBs Direct absorption
– I/I0– sensitivity and selectivity– multiple passes and Cavity Ring Down Spectroscopyor
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
C n
C n
C nU ~ 5 0 0 V
t ~ 1 0 s
p ~ 1 0 b a r
1 % C 2H 2 in A r
U
C n
1 2
2 f ix ed
1 sc an n e d
C n
C n
C n + e
Experimental setupresonant two colour photo detachment
R2CPD
10 12 14 16 18 20 22
C10
H-
C13
H-
C7
-
C4-
in
tens
ity
time-of-flight / s
Massspectrum of the ion source
Anion spectroscopy
AA +e-
Photodetachment
threshold
Dipole bound states -DBSs analogous to Rydberg
states for neutrals - large orbital
requires a minimum dipole moment of ~2-2.5 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 C2nH- (n=2-4)
1 1+ transitions close to the threshold
(EA). binding energies ~200 -
500 cm-1
for C4H- DBS connected to an excited neutral state
(E(2)> E(2+ )) transitions in the UV (no
DIBs) (<350nm)
28000 28500 29000 29500 30000 30500 cm-1
EA
EA
C4H-
29500 30000 30500 31000 31500 32000
C6H-
30000 30500 31000 31500 32000 32500
EA
C8H-
Origin of C4H- (DBS)
rotational resolution, bent upper state
28630 28640 28650 28660 28670 28680 28690
A = 30.5 cm-1
cm-1
K´=1 K´´=0
K´=0 K´´=0
PD-spectrum of l-C3H2- (DBS)
assigned by:K. Yokoyama, Gary W. Leach, Joseph B. Kim, and W. C. Lineberger, J. Chem. Phys. 105, 10696 +10706, 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
Comparison to DIBsLaboratory AstronomicalPeak nm DIB (nm) fwhm (nm) EW (mÅ)A1 699.37(7) 699.32(J) 0.096 116
699.318(G)A3 678.81(7) 678.87(J) 0.087 7
678.866(W) 2.3A4 648.97(1) 649.19(J) 0.076 18
648.962(W) 3.6648.929(T) 0.064 6-12
A5 615.21(2) 615,115(T) 0.144 0-15
B12 496.39(30) 496.40(J) 0.063 16
496.389(T) 0.071 31496.390(K)
C1 498.49(15) 498.47(J) 0.065 11
498,478(T) 0.067 19 498.481 (K)
C3 488.74(30) 488,18(J) 0.135 22
488,04(J) 1.97 611488.256(T) 1.49 >466
J=Jenniskens & Desert (1994), G=Galazutdinov et al. http://www.sao.ru/~gala/DIBwavelength.htm, T= Tuairisg et al. (2000), W = Weselak et al. (2000)
All bands in question are narrow only the origin band is considered strong
– our spectrum overlaps with DIB – the position of the DIB has not changed from
Jenniskens to McCall or Galazutdimov the two spectra from p 10709 don’t agree O° is perturbed (p. 10708- paragraph B) O° is not visible in Yokoyama-> How can McCall / Oka rule out the Match ?