Felix Güthe 1, Hongbin Ding, Thomas Pino 3, Tim W. Schmidt 4, Andrei Boguslavskiy John Maier Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland 1 abcd Switzerland Ltd., Baden, Switzerland 2 Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland 3 Laboratoire de Photophysique Moleculaire, Universite Paris-Sud, Orsay, France 4 Sydney University, Sydney, Australia Bunsentagung, Dresden 2004 Gas phase electronic spectra of linear carbon chains: HC n+1 H, HC n H, HC n+1, HC n

hypothetical new allotrope diamond: sp3 graphite: sp2 “polyyne”: sp hypothetical new allotrope molecular wire precursor nano tubes, fullerenes etc. interstellar molecules optical properties: transition n-> ∞∞ band gap bulk behaviour optical properties: band gaps absorption in the ISM ->spectroscopy Nanowires

taken from: Interstellar molecules

K.-H. Homman, Angew. Chem. 1998, 110, 2572; Angew. Chem. Int. Ed. Engl. 1998, 37, 2435; Flames

Picture : H. Linnartz Pulsed Electrical Discharge

2= 157 nm, 189nm, 212nm Experiment

Mass spectrum

electronic transitions- HC 2n H excitations:   + g  →→ (n)  u / (n-1)  g →→ (n)  g/u A   u (n)  u / (n-1)  g →→ (n)  g/u    + u (n)  u / (n-1)  g →→ (4n)  g/u    u (4n-1)  g/u →→ (n)  g/u    u

HC 2n H(n=8-13):   + g  →→   + u R2CPI-spectra of acetylenic chains

 states: HC 6 H, HC 8 H, HC 10 H, HC 12 H, HC 14 H HC 2n H(n=3-7):   + g →→   u,   - u  dipole-forbidden ( bending)

strong B-transiton! Observed and Calculated Values

electronic transitions- HC 2n+1 H excitations:   - g  →→ (n-1)  g / (n-1)  u →→ (n)  u / (n-1)  g a   - u (n)  u / (n-1)  g →→ (n)  g/u b   - u (n)  u / (n-1)  g →→ (4n+4)  g/u C   u mixing of degenerate a(   - u ) and  b(   - u ) yields    - u )=a+b/sqrt(2)    - u )=a-b/sqrt(2) Dewar-Longuet-Higgins (1954, Proc. Phys. Soc. ) on odd alternant hydrocarbons: A occurs at longer wavelength and is weaker than B B must be the strongest transition

The HC 2n+1 H Series: HC 7 H, HC 9 H, HC 11 H, HC 13 H HC 2n+1 H(n=3-6): X   - g  →→ A   - u,

strong B-transiton HC 19 H is weak in mass spectrum, but still visible HC 13 H... HC 19 H: X   - g  →→ B   - u, MRCI: Mühlhäuser, Peyerimhoff et al. (2002)

HC 13 H... HC 19 H: X   - g  →→ B   - u, as predicited in 1954 !

extrapolation to C 

isoelectronic HC n - system

Solvent and endgroup effect

Conclusions for odd and even chains: strong B-states: –f~Nc –position in the visible –broad peaks –in the ISM –similar for kation (HC 2n+1 H +, HC 2n+1 H - ), anion sp allotrope: bandgap in UV/visible matrix shifts bondlength alternation

HC 2n+1 H: anion - neutral- cation ground state: (n-1)   (n)  (n+ 1)   : (n-1)  (n)  →→ (n-1)  (n)  a   - u (n)  (n+1 )    →→ (n)  (n+1 )     b   - u same behaviour for anions and cations: a and b degenerate-> mixing to yield weak A and strong B transition

Bond length alternation: Acetylenic vs cumulenic

Bond length alternation: even and odd

Bond length alternation: neutral and anionic

backup longchains additional material

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

Ion:D 0 S1S1 S1S1 Neutral:S 0 IP/2 IP common example:“uncommon Example”:C n C n *  C n-m +C m Cn+Cn+ near UV UV vis near UV C n *+  C n-m + +C m exit channels? REMPI scheme

Franck- Condon factors Excitation scheme even odd

strong solvent shift: 4000 cm -1 to the red

HCCH + HCCH - + C HCCH - HCC - C - HC 2n H HC 2n -

R2CPI-spectra of acetylenic chains   + g  →→   + u

Even : HC 6 H, HC 8 H, HC 10 H, HC 12 H, HC 14 H HC 2n H(n=3-7):   + g  →→   u

The HC 2n+1 H Series: HC 7 H, HC 9 H, HC 11 H, HC 13 H... HC 19 H

end polayacetylenes additional material

Gas phase electronic spectra of linear carbon chains: HC n+1 H, HC n H, HC n+1, HC n Felix Güthe 1, Hongbin Ding, Thomas Pino 3, Tim W. Schmidt 4, Andrei Boguslavskiy John Maier Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland 1 abcd Switzerland Ltd., Baden, Switzerland 2 Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland 3 Laboratoire de Photophysique Moleculaire, Universite Paris-Sud, Orsay, France 4 Sydney University, Sydney, Australia Bunsentagung, Dresden 2004

C 3 H- identified in the ISM by microwave spectroscopy! spectrum in the visible detected via R2CPI with F2 laser in the VUV !!

C3HC3H complicated spectrum! Renner-Teller (4 atoms) distorted more than one electronic state

C3HC3H ground state: 2  linear-bend transition 3 electronic states contribute to spectrum complicated Renner- Teller distorted spectrum! individual lines to weak to be detected in the ISM by vis-absorption

electronic transitions- C 2n H excitations:   →→ (4n+1)  →→ (n)    :weak, IR (n-1)  →→ (n)    :strong, vis (n)  →→ (n+1)    :weak UV excitations:   →→ (n)  →→ (4n+1)    (4n+1)  →→ (n+1)    (n)  →→ (n+1)   

The C 2n+1 H Series: C 3 H,C 5 H,C 7 H,C 9 H

electronic transitions- C 2n+1 H excitations:   →→ (4n+3)  →→ (n)           :vis (n-1)  →→ (n)    : vis (n)  →→ (n+1)    :

The C 2n+1 H Series: C 3 H,C 5 H,C 7 H,C 9 H 2  →→             different electronic states!

Extrapolation

end longchains additional material

C 7 H 7 - Tropyl vs. Benzyl 7 ring / 6 ring from stable C 7 H 7 + ion!

C 7 H 7 - Tropyl vs. Benzyl C 6 H 5 CH 2 :C ←← X: tropyl radical –complex spectrum –Jahn-Teller distorted: –D 7h

C 7 H 3 - identification of the structure!

variety of candidates geometries DFT B3LLYP/6_31G* calculation : –energies –rotational constants

C 7 H 3 -rotational K-structure! rotational structure! –down selection: -> 3 member ring –spin statistics : -> isomer 2

C 7 H 3 - structure identified! no methyl group! –unlike C 9 H 3,C 11 H 3,... (Schmidt et al. IJMS 2003)

REMPI aromatics additional material

R2PI-Spectra from Benzene-Discharge

end REMPI

AB + + h -> A + + B, A + detected AB + from source, hscanned for resonance

Fragmentation spectroscopy for van der Waals clusters: M·Ar n + + h -> M M·Ar n Ar,M= HC 4 H

extrapolatio n of band origins

end Fragmentation additional material