Felix Güthe 1, Hongbin Ding, Thomas Pino 3, Tim W. Schmidt 4, Andrei Boguslavskiy John Maier Institut für Physikalische Chemie der Universität Basel, Basel,

Felix Güthe1, Hongbin Ding, Thomas Pino3,

Tim W. Schmidt4, Andrei BoguslavskiyJohn Maier

Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland1 Switzerland Ltd., Baden, Switzerland

2 Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland3 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:

HCn+1H, HCnH , HCn+1 , HCn

hypothetical new allotropediamond: sp3graphite: sp2“polyyne”: sp

hypothetical new allotropemolecular wireprecursor nano tubes, fullerenes etc.interstellar molecules

optical properties:transition n-> ∞∞ band gap bulk behaviour

optical properties: band gapsabsorption in the ISM->spectroscopy

Nanowires

taken from:http://cfa-www.harvard.edu/cfa/mmw/mmwlab/ismmolecules_organic.htmlInterstellar molecules

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

Flames

Picture : H. Linnartz

Pulsed Electrical Discharge

R e so n a n t Tw o P h o to n Io n iz a tio n S p e c tro sc o p y

p ~ 1 0 b a r

1 % C 2H 2 in A r

U

C n

1

2 2 f ix e d

1 s c a n n e d

+-

C n

*

C n

C + en

+ -

C n

+

2= 157 nm, 189nm, 212nm

Experiment

120 240 360 480 600 720 840 960 1080 1200 1320-8

-6

-4

-2

0

C10

C20

C30

C40

C50

C60

C70

C80

C90

C100

C110

C4H

2- Discharge source

C4H

2

C114

C44

C60

Masse (a.m.u.)

Inte

nsity

C24

C25

C24

Hm

Mass spectrum

electronic transitions- HC2nH

excitations: +g→→

(n)u/ (n-1)g →→ (n)g/uAu (n)u/ (n-1)g →→ (n)g/u+

u

(n)u/ (n-1)g →→ (4n)g/uu

(4n-1)g/u →→ (n)g/uu

- -

X1+

g ~

(2n)g

2(n-1)g

4(n)u

4 for n = even

(2n)u

2(n-1)u

4(n-1)g

4 for n = oddlevels have alternating symmetries g and u

HC2n

H

(4n-1)

(n+1)

(n)

(4n)

(n-1)

280 290 300 310 320 330 340 350 360

Wavelength (nm)

HC26

H

HC18

H

HC20

H

HC22

H

HC24

H

HC16

H

HC2nH(n=8-13): +g→→+

u

R2CPI-spectra of acetylenic chains

states: HC6H, HC8H, HC10H, HC12H, HC14H

HC2nH(n=3-7):+g→→u,

-udipole-forbidden ( bending)

280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440

280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440

81

0 HC6H

Wavelength (nm)

41

061

0141

0

31

0141

0141

0

HC10

H

40

1140

1141

0161

0141

0

HC12

H

171

0HC14

H

121

0

22

0121

0

HC8H

0 4 8 12 16 20 24 280

2

4

6

8

10

12

HC2n

H

C 1u-X 1

g

+(Exp.)

A 1u-X 1

g

+(Exp.)

B 1u

+ -X 1g

+(Exp.)

C 1u-X 1

g

+(CASSCF)

B 1u

+ -X 1g

+(CASSCF)

A 1u(1

u

-)-X 1g

+(CASSCF)

Tra

nsiti

on e

nerg

y (e

V)

Number of carbon atoms

strong B-transiton!

Observed and Calculated Values

electronic transitions- HC2n+1H

excitations: -g→→

(n-1)g/ (n-1)u →→ (n)u/ (n-1)ga-u

(n)u/ (n-1)g →→ (n)g/ub-u

(n)u/ (n-1)g→→ (4n+4)g/uCu

mixing of degenerate a(-u) andb(-

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

X1-

g ~

(2n)g

2(n-1)g

4(n)u

2 for n = even

(2n)u

2(n-1)u

4(n-1)g

2 for n = oddlevels have alternating symmetries g and u

HC2n+1

H

(4n-1)

(n+1)

(n)

(4n)

(n-1)

The HC2n+1H Series: HC7H, HC9H, HC11H, HC13H

HC2n+1H(n=3-6): X-g→→ A-

u,

450

475

500

525

550

575

600

625

650

675

700

725

750

41

042

000

0HC13

H

31

033

0

32

0 00

0 HC11

H

*~fragment: HC9H

2-H

*

** **

*

*

32

031

0 00

0 HC9H

23000 22000 21000 20000 19000 18000 17000 16000 15000 14000 13000

21

0

Wavenumber (cm-1)

21

0+41

0

21

0+2b 2b

2a3'2'

1'

00

0

41

0

HC7H00

0

strong B-transiton HC19H is weak in mass spectrum, but

still visible

HC13H ... HC19H: X-g→→ B-

u,

34800 35000 35200 35400 35600 35800 36000 36200

HC13

H 00

0

Wavenumbers (cm-1)

28800 29000 29200 29400 29600 29800 30000 30200

HC19

H00

0

MRCI: Mühlhäuser, Peyerimhoff et al. (2002)5 7 9 11 13 15 17 19

2

3

4

5

6

7

8

9

10

A 3u

- -X 3g

-(Matrix & gas phase)

B 3u

- -X 3g

- (Gas phase)A-X (MRCI)

B-X (MRCI)

C-X (MRCI)C-X (CASSCF)

B-X (CASSCF)

A-X (CASSCF)

Tra

nsiti

on e

nerg

ies

(eV

)

Number of carbon atoms

HC13H ... HC19H: X-g→→ B-

u,

5 7 9 11 13 15 17 19

0

2

4

6

8

10

12

C-X (MRCI)

A-X (MRCI)C-X (CASSCF)

A-X (CASSCF)

B-X (MRCI)

X1000

X100X100

X1000

B-X (CASSCF)O

scill

ator

str

engt

h

Number of carbon atoms

as predicited in 1954 !

extrapolation to C

6056524844403632282420 16 12 8 40

10000

20000

30000

40000

50000

60000

70000

HC2n+1

H (odd): 3-

u¬3-

g:

E (cm-1)= 7152+89094/N ~1398nm3-

u¬3-

g:

E (cm-1)= 17608+232392/N ~567nm

HC2n

H (even): 1+

u,1-

u¬1+

g:

E (cm-1)= 17100+97004/N ~585nm1+

u¬1+

g:

E (cm-1)= 20068+244590/N ~498nm

E (c

m-1)

Ncarbon

isoelectronic HCn- system

6056524844403632282420 16 12 8 40

10000

20000

30000

40000

50000

60000

70000

HC2n

- (even): 3-

u¬3-

g: ac

E (cm-1)= 4926+259048/N ~2030nm3-

u¬3-

g: cum

E (cm-1)= 10096+182895/N ~990nm

DBS: 1+

u¬1+

g:

E (cm-1)= 34262-22591/N ~292nm~EA

HC2n+1

- (odd): 3-

u¬3-

g: ac

E (cm-1)= 8009+178096/N ~1248nm3-

u¬3-

g: cum

E (cm-1)= 14783+129569/N ~676nm

HC2n+1

H (odd): 3-

u¬3-

g:

E (cm-1)= 7152+89094/N ~1398nm3-

u¬3-

g:

E (cm-1)= 17608+232392/N ~567nm

HC2n

H (even): 1+

u,1-

u¬1+

g:

E (cm-1)= 17100+97004/N ~585nm1+

u¬1+

g:

E (cm-1)= 20068+244590/N ~498nm

E (c

m-1)

Ncarbon

Solvent and endgroup effect

6056524844403632 28 24 20 16 12 815000

20000

25000

30000

35000

40000

45000

HC2n

H (even)1+

u¬1+

g: ?

gasphase: E (cm-1)= 20068+244590/N ~498nmNe-Matrix :E (cm-1)= 19000+241578/N ~526nmmethanol: E (cm-1)= 16885+237195/N ~592nmacetonitril: E (cm-1)= 18905+195460/N ~528nm

E (c

m-1)

Ncarbon

Conclusions for odd and even chains: strong B-states:

– f~Nc– position in the visible – broad peaks– in the ISM – similar for kation (HC2n+1H+, HC2n+1H-), anion

sp allotrope: bandgap in UV/visible matrix shifts bondlength alternation

HC2n+1H: 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

X1-

g ~

(2n)g

2(n-1)g

4(n)u

1,2,3 for n = even

(2n)u

2(n-1)u

4(n-1)g

1,2,3 for n = odd

Ions:

HC2n+1

H+,0,-

(4n-1)

(n+1)

(n)

(4n)

(n-1)

Bond length alternation: Acetylenic vs cumulenic

0 1 2 3 4 5 6 7 8 9 10 11 12 131.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

Ethine

Ethene

Allene

even: HC

10H

HC26

Hodd:

C9

Bond length alternation in the polyacetylenic chains:

"triple"

"single"

Bond

leng

th (Å

)

C-C bond

Bond length alternation: even and odd

0 1 2 3 4 5 6 7 8 9 10 11 12 131.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

Ethine

Ethene

Allene

even: HC

10H

HC26

Hodd:

HC13

H C

9

Bond length alternation in the polyacetylenic chains:

"triple"

"single"

Bond

leng

th (Å

)

C-C bond

Bond length alternation: neutral and anionic

0 1 2 3 4 5 6 7 8 9 10 11 12 131.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

Ethine

Ethene

Allene

even: HC

10H

HC26

H

HC10

-

odd: HC

13H

HC9

-

C9

Bond length alternation in the polyacetylenic chains:

"triple"

"single"

Bond

leng

th (Å

)

C-C bond

backup longchains additional material

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

Ion:D0

S1

S1

Neutral:S0

IP/2

IP

common example: “uncommon Example”:Cn

Cn*Cn-m +Cm

Cn+

near UV

UV

vis

near UV

Cn*+Cn-m

+ +Cm

exit channels?

REMPI scheme

0

2

4

6

8

10

12

14

[1+1'] 2 colour scheme for REMPI on polyacetylenes

UV Excitation

IP

VUV Ionisation

A (1-

u; 1

u)

IC ~ nsIC < ps

X (2u)

cation

B(1+

u)

X(1+

g)En

ergie

(eV

)

R

Franck-Condon factors

Excitation scheme

even

odd

10 12 14 16 18 20 22 24 26 28

26000

28000

30000

32000

34000

36000

38000

40000

Gas - matrix ~1300 cm-1

Gas - solvent ~3500 cm-1

Solvent shifts

HCnH: 1+

u¬1+

g

Neon Matrix Gas phase Methanol

Wav

enum

bers

(cm

-1)

Number of carbon atoms n

strong solvent shift:4000 cm-1 to the red

0 5 10 15 20 251.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

1.38

1.40

Ethine

Ethene

Allene

Bond length alternation in the polyacetylenic chains:

HC26

H and HC10

-

"triple"

"single"

Bond

leng

th (Å

)

C-C bond

HC26

H

HC10

-

HC CH

+HC CH

-

+

CHC CH-

HC C-

HC C

-

HC2nH

HC2n-

0 1 2 3 4 5 6 7 8 9 101.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

1.38

1.40

Ethine

Ethene

Allene

Bond length alternation in the polyacetylenic chains:

HC10

H and HC10

-

"triple"

"single"

Bond

leng

th (Å

)

C-C bond

HC10

H B3LYP

HC10

- MP2

R2CPI-spectra of acetylenic chains +

g→→+u

Even : HC6H, HC8H, HC10H, HC12H, HC14H

HC2nH(n=3-7): +g→→u

280 290 300 310 320 330 340

80

1

HC6H

Wavelength (nm)

290 300 310 320 330 340

20

2120

1

HC8H

320 330 340 350 360 370 380

40

160

1140

1 30

1140

1 140

1

HC10

H

350 360 370 380 390 400 410

40

1140

114

0

1160

114

0

1

HC12

H

380 390 400 410 420 430 440

170

1

HC14

H

120

1zoom

The HC2n+1H Series: HC7H, HC9H, HC11H, HC13H ... HC19H

13000 14000 15000 16000 17000 18000 19000

53

24

1HC

13H

Wavenumber (cm-1)

15000 16000 17000 18000 19000 20000 21000 22000

64

3 75

21

HC11

H

17000 18000 19000 20000 21000 22000 23000

*** * *

*

* 32

1

HC9H

19000 19500 20000 20500 21000 21500 22000 22500 23000

11

109

765

323'

2'1'

18

4HC7H

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28100

150

200

250

300

350

400

450

500

550

600

Neutral

HC2n

H : 1+

u¬1+

gAnions

Ac. HC2n

- : 1+¬1+

HC2n

H

CNH-

Wav

elen

gth

(nm

)

Number of carbon atoms

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28100

150

200

250

300

350

400

450

500

550

600

Neutral

HC2n

H : 1+

u¬1+

g

Anions

Ac. HC2n

- : 1+¬1+

Cum. HC2n

-

Ac. HC2n-1

- : 3-¬3-

Cum. HC2n-1

- :1A'¬1A'

HC2n

H

CNH-

Wav

elen

gth

(nm

)

Number of carbon atoms

end polayacetylenes additional material

Gas phase electronic spectra of linear carbon chains:

HCn+1H, HCnH , HCn+1 , HCn

Felix Güthe1, Hongbin Ding, Thomas Pino3,

Tim W. Schmidt4, Andrei BoguslavskiyJohn Maier

Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland1 Switzerland Ltd., Baden, Switzerland

2 Institut für Physikalische Chemie der Universität Basel, Basel, Switzerland3 Laboratoire de Photophysique Moleculaire, Universite Paris-Sud, Orsay, France

4 Sydney University, Sydney, Australia

Bunsentagung , Dresden 2004

C3H- identified in the ISM by microwave spectroscopy!

spectrum in the visible detected via R2CPI with F2 laser in the VUV !!

cm-1

C10

C3H

C3D

540 520 500 480 460 440 420 400 380 360nm

C3H

complicated spectrum! Renner-Teller (4 atoms) distortedmore than one electronic state

19000 20000 21000 22000

40

1

00

0

40

3

00

0

cm-1

40

2

40

1

Inte

nsit

y (a

.u.)

20880 20910

A2A'(K'=2)--X/

A2A'(K'=2)--X/close-up 40

2 band

C3H

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

60 80 100 120 140 160 180 200 220 240 260 280 300

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

2+

2

2-

2

2

Ene

rgy

(eV

)

CCH angle°60 80 100 120140 160180 200220 240260 280300

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

F

E

D

C

BA

X

2+

2

2-

2

2

En

ergy (

eV

)

CCH angle°

electronic transitions- C2nH

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)

X2~

(n-1)4(4n+1)2(n-1)3

ground stateC

2nH for n>2

(4n+1)

(n+1)

(n)

(4n+2)

(n-1)

X2~ for n < 2

(n-1)4(n)4(4n+1)1

ground stateC

2nH for n<2

(4n+1)

(n+1)

(n)

(4n+2)

(n-1)

The C2n+1H Series: C3H,C5H,C7H,C9H

360 390 420 450 480 510 540 570 600

C2A'' --X2

B2A'' --X2

00

0

00

0

A2A' --X20

0

0

nm

C5H

C7H

C9H

C3H

Inte

nsit

y (a

.u.)

00

0

D2 --X2

B2- --X2

B2- --X2A2 --X2

100

2

100

19

0

10

0

0

00

011

0

1 00

0

C2+ --X200

0

C2+ --X2A2 --X2

130

100

00

0

0

00

0

F2 --X27

0

1

electronic transitions- C2n+1H

excitations: →→

(4n+3)→→ (n):vis

(n-1)→→ (n): vis

(n)→→ (n+1):

X2~

(n-1)4(4n+3)2(n)1

C2n+1

H

(4n+3)

(n+1)

(n)

(4n+4)

(n-1)

The C2n+1H Series: C3H,C5H,C7H,C9H

2→→ -3- 4 different electronic

states!

360 390 420 450 480 510 540 570 600

C2A'' --X2

B2A'' --X2

00

0

00

0

A2A' --X20

0

0

nm

C5H

C7H

C9H

C3H

Inte

nsit

y (a

.u.)

00

0

D2 --X2

B2- --X2

B2- --X2A2 --X2

100

2

100

19

0

10

0

0

00

011

0

1 00

0

C2+ --X200

0

C2+ --X2A2 --X2

130

100

00

0

0

00

0

F2 --X27

0

1

Extrapolation

60575451484542393633302724211815 12 9 6 35000

10000

15000

20000

25000

HC2n+1

(odd):

A 2¬2B 2-¬2C 2+¬2HC

2n(even):

2¬2:

E (cm-1)= 6830+72144/N ~1464nm

E (c

m-1)

Ncarbon

end longchains additional material

C7H7- Tropyl vs. Benzyl

7 ring / 6 ring from stable C7H7+ ion!

26000 27000 28000 29000 30000 31000 32000

26000 27000 28000 29000 30000 31000 32000

cm-1

C7H

7

from cycloheptatriene/ Ar

C7H

7

from benzene/ Ar

C7D

7

from d6-benzene/ Ar

32000 32500 33000

C X

cm-1

32000 32500 33000

toluene / Ar

cycloheptatriene / Ar

C7H7- Tropyl vs. Benzyl

C6H5CH2:C ←←X:tropyl radical

–complex spectrum –Jahn-Teller distorted:

–D7h

''2

2''3

2 EE ¬

C7H3- identification of the structure!

variety of candidates

geometries DFT B3LLYP/6_31G*

calculation :–energies–rotational constants

C7H3-rotational K-structure!

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

19000 20000 21000 22000 23000 cm-1

1211

10

9

8

7

65

4

3

2

1

1'

m/z

=87

Ion

Cur

rent

(ar

b.)

18890 18900 18910

b.Sim

a.Exp

close-up of band 1

C7H3- structure identified!

no methyl group! – unlike C9H3 ,C11H3 ,... (Schmidt et al. IJMS 2003)

REMPI aromatics additional material

96 108 120 132 144 156 168 180

F2-Laser: 157nm

Mass (amu)

C8

C9

C10

C11

C12

C13

C14

C15

C14

H10

C10

H8

R2PI: 278-290nm

34600 34800 35000 35200 35400 35600 35800 36000

S 2¬S 0: p

hen

a(B2u

)

A(B1u

)b(B

2u)

B(B1u

)

00

0

300

1

290

1

280

1 430

1 420

1

260

1

250

1 230

1210

1

00

0

412

0

291

0281

0

271

0

261

0

251

0

241

0

171

0181

0

278279280281282283284285286287288

00

0a

b

m/z = 178

wavenumber / cm-1

m/z = 116

m/z = 104

wavelength / nm

m/z = 102

R2PI-Spectra from Benzene-Discharge

00

0

a1

a1

b2

a1 a

1

a1

a1 a

1

a1

1 23

4

Nap

ht. 0

0 0

IP(N

apht

. )/2

Nap

ht. 4

0 1

Nap

ht. 7

0 1 8

Nap

ht. 8

0 1 70 1 8

0 1

279281283285287289291293295297299301

00

0

291

0

281

0

422

0

251

0

241

0

191

0

170

1

33000 33400 33800 34200 34600 35000 35400 35800

m/z = 166

wavenumber / cm-1

m/z = 128

CH3

wavelength / nm

m/z = 118

R2PI-Spectra from Benzene-Discharge

1 2

54

3

trans cis

cis trans

end REMPI

P h o to F ra g m en ta tio n E x p e rim en t fo r C a tio n s

p ~ 1 0 b a r

1 % C 2H 2 in A r

U

1 2

C m

R E T O F a s tan d e m M S w ith d o u b le m ass se le c tio n !

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

Fragmentation spectroscopy for van der Waals clusters: M·Arn

+ + h -> M M·Arn-1+ + Ar, M= HC4H

19600 19700 19800 19900 20000

frequency (cm-1)

19600 19700 19800 19900 20000

19600 19700 19800 19900 20000

19000 19500 20000 20500 21000 21500 22000 22500 23000

n = 2

n = 4

n = 3

n = 1

frequency (cm-1)

HC4H Ar

n

extrapolation of band origins

end Fragmentation additional material