The 68th International Symposium on Molecular Spectroscopy
Structure Determination of Non-Linear
Hydrocarbon Chains by Deuterium Labelling
D. Zhao, H. Linnartz
Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, the Netherlands;
M.A. Haddad, W. Ubachs
Department of Physics and Astronomy, LaserLaB,VU University Amsterdam, the Netherlands;
Columbus, June 19, 2013
Molecules in the (dense) Interstellar Medium or Circumstellar Shells
2 atoms
H2
AlF
AlCl
C2**
CH
CH+
CN
CO
CO+
CP
SiC
HCl
KCl
NH
NO
NS
NaCl
OH
PN
TiO
SO
SO+
SiN
SiO
SiS
CS
HF
HD
FeO ?
O2
CF+
SiH ?
PO
AlO
OH+
CN–
SH+
SH
HCl+
3 atoms
C3*
C2H
C2O
C2S
CH2
HCN
HCO
HCO+
HCS+
HOC+
H2O
H2S
HNC
HNO
MgCN
MgNC
N2H+
N2O
NaCN
TiO2
OCS
SO2
c-SiC2
CO2*
NH2
H 3+ *
H2D+,
HD2+
SiCN
AlNC
SiNC
HCP
CCP
AlOH
H2O+
H2Cl+
KCN
FeCN
HO2
4 atoms
c-C3H
l-C3H
C3N
C3O
C3S
C2H 2 *
NH3
HCCN
HCNH+
HNCO
HNCS
HOCO+
l-C3H+
5 atoms
C5*
C4H
C4Si
l-C3H2
c-C3H2
H2CCN
H2CO CH4*
H2CN HC3N
H2CS HC2NC
HCOOH
H3O +
c-SiC3 H2CNH
H2C2O
CH3*
–
H2NCN
C3N
PH3 ? HNC3
HCNO SiH4*
+
HOCN H2COH
–
HSCN C4H
HC(O)CN
H2O 2
HNCNH
CH3O+
6 atoms
C5H
l-H2C4
C2H4*
CH3CN
CH3NC
CH3OH
CH3SH
HC3NH+
HC2CHO
NH2CHO
C5N
l-HC4H*
l-HC4N
c-H2C3O
H2CCNH (?)
C5N–
7 atoms
8 atoms
9 atoms
C6 H
CH2CHCN
CH3C2H
HC5N
CH3CHO
CH3NH2
c-C2H4O
H2CCHOH
C6H–
CH3C3N
HC(O)OCH3
CH3COOH
C 7H
H 2C 6
CH2OHCHO
l-HC6H*
CH2CHCHO
CH2CCHCN
H2NCH2CN
CH3C4H
CH3CH2CN
(CH3)2O
CH3CH2OH
HC7N
C8H
CH3C(O)NH2
C8H–
C3H6
11 atoms
HC9N
CH3C6H
C2H5OCHO
12 atoms
C 6H 6 *
C2H5OCH3 ?
n-C3H7CN
>12 atoms
HC11N
C60*
C70*
NHCHCN
10 atoms
CH3C5N
(CH3)2CO
(CH2OH)2
CH3CH2CHO
(www.cdms.de)
Hydrocarbons in Plasma and Flame
(Angew. Chem. Int. Ed., 1998, 37, 2434-2451)
(Prog. Energy Com. Sci., 2000, 26, 565-608)
Carbon chain species, both linear and nonlinear, are suggested as
precusors and important intermediates in the formation of PAHs.
Spectroscopic characterization of molecular structure
Linear molecules:
Rotational resolved spectrum at high resolution
Bond length, electronic configuration, vibrational motion…
Non-linear molecules
Complex electronic-vibrational-rotational struction,
Intramolecular interactions
Always partially resolved (even unresolved), particularly in the visible region
Example: C9H3 and C11H3
Mass-selective REMPI:
Structure determination not available.
(Schmidt et al., Int. J. Mass Spectr., 2003, 107, 6550)
(Zhang, J. Cehm. Phys., 2004, 121, 8212)
High-resolution CRDS:
K-stack structure and partially resolved
rotational structure, suggesting the likely C9H3
structure:
(Zhao et al., Chem. Phys. Lett., 2011, 501, 232)
Experiment
Systematic deuterium-labeling experiments are performed to
characterize molecular structures of C9H3 and C11H3.
 Pulsed cavity ring-down spectroscopy
 A pinhole pulsed discharge nozzle to produce
large hydrocarbon chains in a plasma jet
 Deuterium labeling
(Zhao et al., Chem. Phys. Lett., 2011, 501, 232)
 C9H3 and C11H3 by discharging C2H2/He
 C9D3 and C11D3 by discharging C2D2/He
 All deuterated isotopologues by discharging (C2H2+C2D2)/He, with known H/D
isotope ratio, typically H/D~1.
Fully hydrogenated and deuterated spectra
18881.41
18920.20
19312.92
(blended with
C2 Swan band)
(C6H)
18950.96
19349.08
18988.10
19383.9
Band contour analyses result in:
Indicative rotational constants (A, B, C)
Lowest lying bending vibration (ν)
(Zhao et al., J. Chem. Phys., 2011, 135, 074201)
Three cases in D-substitution of CnH3
Assuming that in a plasma environment with high electronic temperature, hydrogenation
and deuteration in the molecule have the same probability, i.e., zero-point effect can be
neglected.
HII
Due to molecular symmetry
 Cs or C1: three H atoms are NON-interchangeable to each other
Eight isotopologues are expected with the equal production
probability: HHH, HHD, HDH, DHH, HDD, DHD, DDH, DDD
HI
 C2v or C2: Two H atoms are interchangeable to each other (e.g., HI and HIII)
Six isotopologues are expected: HHH, HHD=DHH, HDH, HDD=DDH, DHD, DDD,
where HHD and HDD have two times production probability than other four;
 C3v or D3h: All Three H atoms are interchangeable to each other
Four isotopologues are expected: HHH, HHD=HDH=DHH, HDD=DHD=DDH, DDD,
where H2D and HD2 have three times production probability than H3 and D3.
HIII
C9H3: C2v case
For both origin and bending
vibronic band transitions
ΔH/DI = +34.90 cm-1
ΔH/DII = -1.04 cm-1
H/D ~1
Combined with DFT-B3LYP calculations on
rotational constants(A, B, C), electronic
transition energy, and low-lying bending
vibration, molecular structure is determined as:
(Zhao et al., J. Chem. Phys., 2011, 135, 074201)
C11H3: C2v case
H/D ~1
ΔH/DI = +34.9 cm-1
( identical to C9H3)
ΔH/DII = -0.6 cm-1
( half of Δ (C9H3) )
 Isotope shifts structure
similarities and differences
 DFT-B3LYP calculations
(Zhao et al., J. Chem. Phys., 2011, 135, 074201)
C11H3: Cs case ?
A red shift of ~ 70 nm is expected for Cs-C11H3 with respect to C2vC9H3, due to the ‘particle-in-a-box’ behavior that has been found for
linear carbon chains previously, and also DFT calculations.
Cs-C11H3
 no mass selective spectroscopic information reported;
 Searched in the expected wavelength region.
H/D ~0.7
Large carbon chains
not favored.
 Red shift with respect to C2v-C9H3: ~66.2 nm
 Isotopic shift:
ΔI = +30.6 cm-1, ΔII = -0.7 cm-1 (close to values for C9H3)
ΔIII = +13.6 cm-1
 Rotational constants, low-lying bending vibration, and band position are consist
with DFT-B3LYP calculations on Cs-C11H3
(Zhao et al., J. Chem. Phys., 2012, 136, 054307)
Conclusion: unraveling of the puzzle
(see Zhao et al., J. Chem. Phys., 2012, 136, 054307)
Conclusions
 Structure
determinations by systematic deuterium labeling
experiments on
 C9H3 with C2v symmetry
 Two C11H3 isomers with C2v and Cs symmetries, respectively.
 This result also confirms that optical spectra of D-substituted
species can provide molecular symmetry information of
polyhydrides, as well as chemical bond correlations in the
substructures containing D-labeled hydrogen.
 Deuterium labeling is considered as a useful approach to
characterize the molecular structure of gaseous hydrocarbons.
Acknowledgements
 FOM
 NWO
 The Dutch Astrochemistry Network
 Stefan Schlemmer (C2D2 flasks)