Gas phase electronic spectra of linear carbon chains: HCn 1H, HCnH , HCn 1 , HCn - PowerPoint PPT Presentation

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Gas phase electronic spectra of linear carbon chains: HCn 1H, HCnH , HCn 1 , HCn

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Gas phase electronic spectra of linear carbon chains: HCn+1H, HCnH , HCn+1 , HCn Felix G the1, Hongbin Ding, Thomas Pino3, Tim W. Schmidt4, Andrei Boguslavskiy – PowerPoint PPT presentation

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Title: Gas phase electronic spectra of linear carbon chains: HCn 1H, HCnH , HCn 1 , HCn


1
Gas phase electronic spectra of linear carbon
chains HCn1H, HCnH , HCn1 , HCn
Felix Güthe1, Hongbin Ding, Thomas Pino3, Tim
W. Schmidt4, 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
2
Nanowires
hypothetical new allotrope molecular
wire precursor nano tubes, fullerenes
etc. interstellar molecules
hypothetical new allotrope diamond
sp3 graphite sp2 polyyne sp
optical properties band gaps absorption in the
ISM -gtspectroscopy
optical properties transition n-gt 88 band gap
bulk behaviour
3
Interstellar molecules
taken from http//cfa-www.harvard.edu/cfa/mmw/mmw
lab/ismmolecules_organic.html
4
Flames
K.-H. Homman, Angew. Chem. 1998, 110, 2572
Angew. Chem. Int. Ed. Engl. 1998, 37, 2435
5
Pulsed Electrical Discharge
Picture H. Linnartz
6
Experiment
l2 157 nm, 189nm, 212nm
7
Mass spectrum
8
electronic transitions- HC2nH
excitations 1Sg ?? (n)pu/ (n-1)pg ??
(n)pg/u A1Du (n)pu/ (n-1)pg ?? (n)pg/u
B1Su (n)pu/ (n-1)pg ?? (4n)sg/u
1Pu (4n-1)sg/u ?? (n)pg/u 1Pu
9
R2CPI-spectra of acetylenic chains
HC2nH(n8-13) 1Sg ??1Su
10
D states HC6H, HC8H, HC10H, HC12H, HC14H
  • HC2nH(n3-7)1Sg??1Du, 1S-u dipole-forbidden (np
    bending)

11
Observed and Calculated Values
strong B-transiton!
12
electronic transitions- HC2n1H
excitations 3S-g ?? (n-1)pg/ (n-1)pu ??
(n)pu/ (n-1)pg a3S-u (n)pu/ (n-1)pg ??
(n)pg/u b3S-u (n)pu/ (n-1)pg ?? (4n4)sg/u
C3Pu
mixing of degenerate a(3S-u) and b(3S-u)
yields A(3S-u ) ab/sqrt(2) B(3S-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

13
The HC2n1H Series HC7H, HC9H, HC11H, HC13H
  • HC2n1H(n3-6) X 3S-g ?? A 3S-u,

14
HC13H ... HC19H X 3S-g ?? B 3S-u,
  • strong B-transiton
  • HC19H is weak in mass spectrum, but still visible

MRCI Mühlhäuser, Peyerimhoff et al. (2002)
15
HC13H ... HC19H X 3S-g ?? B 3S-u,
  • as predicited in 1954 !

16
extrapolation to C
17
isoelectronic HCn- system
18
Solvent and endgroup effect
19
Conclusions
  • for odd and even chains strong B-states
  • fNc
  • position in the visible
  • broad peaks
  • in the ISM
  • similar for kation (HC2n1H, HC2n1H-), anion
  • sp allotrope bandgap in UV/visible
  • matrix shifts
  • bondlength alternation

20
HC2n1H anion - neutral- cation
  • ground state (n-1)p4(n)p1,2,3 (n1)p0
  • (n-1)p4(n)p1,2,3 ?? (n-1)p3(n)p2,3,4 a3S-u
  • (n)p1,2,3 (n1)p0 ??(n)p0, 1,2 (n1)p1 b3S-u
  • same behaviour for anions and cations
  • a and b degenerate-gt mixing to yield
  • weak A and
  • strong B transition

21
Bond length alternation Acetylenic vs cumulenic
22
Bond length alternation even and odd
23
Bond length alternation neutral and anionic
24
backup longchains
  • additional material

25
Spectroscopic techniques
  • Spectral range UV/visible for DIBs
  • Direct absorption
  • I/I0
  • 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

26
REMPI scheme
Cn
Cn Cn-m Cm
IonD0
Cn Cn-m Cm
IP
UV
exit channels?
S1
IP/2
near UV
near UV
S1
vis
NeutralS0
common example
uncommon ExampleCn
27
Excitation scheme
Franck-Condon factors
even
odd
28
strong solvent shift 4000 cm-1 to the red
29
-
HC
C
-
HC
C
HC2n-

-
HC
CH
HC
CH

-
HC
CH
C
HC2nH
30
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31
R2CPI-spectra of acetylenic chains
1Sg ??1Su
32
Even D HC6H, HC8H, HC10H, HC12H, HC14H
  • HC2nH(n3-7) 1Sg ??1Du

33
The HC2n1H Series HC7H, HC9H, HC11H, HC13H ...
HC19H
34
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35
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36
end polayacetylenes
  • additional material

37
Gas phase electronic spectra of linear carbon
chains HCn1H, HCnH , HCn1 , HCn
Felix Güthe1, Hongbin Ding, Thomas Pino3, Tim
W. Schmidt4, 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
38
C3H- identified in the ISM by microwave
spectroscopy!
  • spectrum in the visible detected via R2CPI with
    F2 laser in the VUV !!

39
C3H
  • complicated spectrum!
  • Renner-Teller (4 atoms) distorted
  • more than one electronic state

40
C3H
  • ground state 2P
  • 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

41
electronic transitions- C2nH
excitations 2P ?? (4n1)s ?? (n)p 2S weak,
IR (n-1)p ?? (n)p 2P strong, vis (n)p ??
(n1)p 2P weak UV excitations 2S ??
(n)p ?? (4n1)s 2P (4n1)s ?? (n1)p
2P (n)p ?? (n1)p 2S
42
The C2n1H Series C3H,C5H,C7H,C9H
43
electronic transitions- C2n1H
excitations 2P ?? (4n3)s ?? (n)p 2D, 2S-,
2Svis (n-1)p ?? (n)p 2P vis (n)p ?? (n1)p
2P
44
The C2n1H Series C3H,C5H,C7H,C9H
  • 2P ?? 2D, 2S-, 2S, 2P -
  • 3- 4 different electronic states!

45
Extrapolation
46
end longchains
  • additional material

47
C7H7- Tropyl vs. Benzyl
  • 7 ring / 6 ring from stable C7H7 ion!

48
C7H7- Tropyl vs. Benzyl
  • C6H5CH2C ??X
  • tropyl radical
  • complex spectrum
  • Jahn-Teller distorted
  • D7h

49
C7H3- identification of the structure!
50
variety of candidates
  • calculation
  • energies
  • rotational constants
  • geometries DFT B3LLYP/6_31G

51
C7H3- rotational K-structure!
  • rotational structure!
  • down selection -gt 3 member ring
  • spin statistics -gt isomer 2

52
C7H3- structure identified!
  • no methyl group!
  • unlike C9H3 ,C11H3 ,... (Schmidt et al. IJMS 2003)

53
REMPI aromatics
  • additional material

54
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55
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56
R2PI-Spectra from Benzene-Discharge
57
R2PI-Spectra from Benzene-Discharge
58
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59
end REMPI
60
  • AB hn -gt A B , A detected
  • AB from source, hn scanned for resonance

61
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62
Fragmentation spectroscopy
  • for van der Waals clusters
  • MArn hn -gt M MArn-1 Ar, M HC4H

63
  • extrapolation of band origins

64
end Fragmentation
  • additional material
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