1. Photodetachment spectrum of l-C3H2-: The role of dipole bound states for electron attachment in interstellar clouds
F. Güthe*1,3, M. Tulej2,3, and J. P. Maier3
1 Alstom Schweiz, Baden, Switzerland 2 Paul Scherrer Institut, Villigen, Switzerland
3 Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland *
Experimental Setup1 of the
R2CPD gas phase experiment:
Electronic spectrum of l-C3H2-
The electronic spectrum of the linear propadienylidene anion l-C3H2- has been recorded at 50 K by resonance enhanced two photon detachment spectroscopy. This resembles the absorption spectrum to a dipole bound state involving bound-bound and bound-free transitions as well as to Feshbach states.
Electronic Feshbach state
Dipole bound state
To explain the abundance of this carrier in interstellar clouds the ratio of anions to neutrals is estimated for small polar molecules with high electron affinities using chemical considerations.
Bound states (below the detachment threshold)
can only be seen if a second photon is absorbed!
-> Two colour two photon detachment (R2CPD)
An appreciable amount of anions can result in diffuse clouds because the electron attachment to polar molecules is enhanced via dipole bound states.
CnH Pics
experimental : 3 cases
slide
C4H to C8H
C4H to C4D HIRES
Feshbach things
general DBS things polar +e- denstiy
In interstellar conditions only the K =1¬0 components should be visible in absorption
DIB comparison
Laboratory Astronomical
Peak nm DIB (nm) fwhm (nm) EW (mÅ)
A (7) (J)
(G)
A (7) (J)
(W) 2.3
A (1) (J)
(W) 3.6
(T)
A (2) 615,115(T)
B (30) (J)
(T)
(K)
C (15) (J)
498,478(T)
(K)
C (30) 488,18(J)
488,04(J)
(T) >466
References:
Tulej, M.; Güthe, F.; Schnaiter, M.; Pachkov, M. V.; Kirkwood, D. A.; Maier, J. P.; Fischer, G. J. Phys. Chem. A 1999, 103, 9712.
Güthe, F.; Tulej, M.; Pachkov, M. P.; Maier, J. P. Astrophys. J , 555, (2001)
Yokoyama, K., Leach, G. W., Kim, J. B., & Lineberger, W. C., 1996, J. Chem. Phys., 105, and 10706