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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
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
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
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
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
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-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
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
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