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Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
HIGH RESOLUTION INFRARED SPECTROSCOPY AND
SEMI-EXPERIMENTAL STRUCTURES OF Si2C3 AND Ge2C3
Volker Lutter, Laborastrophysik, Universität Kassel, Germany
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Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Theoretical Investigation• C-chains and C-X-chains in quantum chemistry (ab initio methods)
Extensively studied by Botschwina et al.
Experimental Investigation• C-chains and C-X-chains in the gas phase (Inert gas matrices and small XC, XC2 excluded)
Cn: n=3,4,5,6,7,8,9,10,13 (IR, Saykally et al., Giesen et al.)
SiCn: n=3,4,5,6,7,8 (mostly FTMW, SiC4 also Infrared)SCn: n=4,5,6,7,8,9 (FTMW)
SiCnS: n=2,3,4,6(FTMW)
• Symmetric carbon hetero clustersSCnS: n=3SiCnSi: n=3
Motivation
Experimental data from symmetric hetero clusters are underrepresentedfor linear carbon hetero clusters
no permanent dipole moment
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Structural (Fundamental) Chemistryand Symmetric Molecules
Advantage• Symmetric molecules exhibit less different bond lengths• Less parameters enable
1. Higher possible computational levels (ab initio)2. Lower computational costs at the same level of theory
• Symmetric chain like X2C3 molecules provide benchmarks for quantum theory
Disadvantage• Symmetric molecules do not have a permanent dipole moment
1. Not accessible through microwave measurements2. Experimental data need to be taken from infrared measurements
How can we get access to symmetric carbon chain like hetero clusters?
Which feedback can these data give to theoretical structure chemistry?
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Experimental Setup
IR
Nd:YAG
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
In preparation, Lutter et. al.
J. Krieg et al. Rev. Sci. Instrum. 82, 063105 (2011)S. Thorwirth, V.Lutter et al ., J. Mol. Spectrosc. 270, 75-78 (2011)
MeasurementsMain Isotopologue of Si2C3
n3 = 1968.18865(14) cm-1
B0 = 946.378(39) MHza3 = 4.116(55) MHza7 = -3.30(11) MHz
ab inition3 = 1904.8 cm-1 (CCSD(T)/cc-pV(T+d)Z)a3 = 4.239 MHz (CCSD(T)/ cc-pV(Q+d)Z)a7 = -2.61 MHz (CCSD(T)/ cc-pV(Q+d)Z)DB0 =-1.679 MHz (CCSD(T)/ cc-pV(Q+d)Z)All Carbon Substituted Si2
13C3
n3 = 1892.7750(2) cm-1
B0 = 940.412(104) MHza3 = 4.105(144) MHz
ab inition3 =1981.0 cm-1 (CCSD(T)/ cc-pV(T+d)Z)a3 = 4.063 MHz (CCSD(T)/ cc-pV(Q+d)Z)DB0 = -1.586 MHz (CCSD(T)/ cc-pV(Q+d)Z)
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
In preperation, Lutter et. al.
J. Krieg et al. Rev. Sci. Instrum. 82, 063105 (2011)S. Thorwirth, V.Lutter et al ., J. Mol. Spectrosc. 270, 75-78 (2011)
MeasurementsMain Isotopologue of Si2C3
n3 = 1968.18865(14) cm-1
B0 = 946.378(39) MHza3 = 4.116(55) MHza7 = -3.30(11) MHz
ab inition3 = 1904.8 cm-1 (CCSD(T)/cc-pV(T+d)Z)a3 = 4.239 MHz (CCSD(T)/ cc-pV(Q+d)Z)a7 = -2.61 MHz (CCSD(T)/ cc-pV(Q+d)Z)DB0 =-1.679 MHz (CCSD(T)/ cc-pV(Q+d)Z)All Carbon Substituted Si2
13C3
n3 = 1892.7750(2) cm-1
B0 = 940.412(104) MHza3 = 4.105(144) MHz
ab inition3 =1981.0 cm-1 (CCSD(T)/ cc-pV(T+d)Z)a3 = 4.063 MHz (CCSD(T)/ cc-pV(Q+d)Z)DB0 = -1.586 MHz (CCSD(T)/ cc-pV(Q+d)Z)
Semi-Experimental semiBe = 944.700 MHzae-CCSD(T)/cc-pwCVQZ calcBe = 945.903 MHz-----------------------------------------------------------------------------------------------------
deviation 1.203 MHz
semiBe = expB0 -calcDB0
ae-CCSD(T)/cc-pwCVQZ rC-C 1.2895 Å rSi-C= 1.6829 Å
Semi-Experimental semiBe = 938.827 MHzae-CCSD(T)/cc-pwCVQZ calcBe = 940.032 MHz--------------------------------------------------------------------------------------------------------
deviation 1.205 MHz
semiBe = expB0 - calcDB0
ae-CCSD(T)/cc-pwCVQZ rC-C 1.2895 Å rSi-C= 1.6829 Å
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
What happens for larger atoms?1. More electrons to be computed2. Higher computational costs3. Larger influence of electron correlations4. Stronger relativistic effects
Exchanging silicon atoms by germanium atoms5. Ge2C3 has same geometry as Si2C3
6. Same electronic configuration 1Sg
7. Comparable vibrational dipole moment (C-C asym. stretch.)8. Matrix isolation measurement available (vibrational studies)
E. Gonzalez, C. M. L. Rittby, W. R. M. Graham, J. Phys. Chem. 112, 43, 10831-10837, (2008)
One Step Further
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Main Isotopologue
Experimental 74GeC374Ge
n3 = 1932.08997(9) cm-1
B0 = 355.811(27) MHza3 = 1.593(38) MHz
ab initio (CCSD(T)/cc-pVTZ)n3 = 1943.0 cm-1
a3 = 1.532 MHz DB0 = -0.691 MHz
semiBe = 355.121 MHzCCSD(T)/cc-pwCVQZ
calcBe = 355.385 MHz
semiBe = expB0 -calcDB0
Measurements
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Measurements74GeC3
74GeB0=355.811(27)a3=1.593(28)
74GeC372Ge
B0=360.585(20)a3=1.612(38)
74GeC370Ge
B0=365.487(96)a3=1.628(138)
72GeC372Ge
B0=365.494(31)a3=1.625(43)
72GeC370Ge
B0=370.480(126)a3=1.648(177)
70GeC370Ge
B0=375.544(333)a3=1.663(474)
Experimental
DB0 =-0.691calca3 = 1.532
DB0 =-0.699calca3= 1.554
DB0 =-0.708 calca3= 1.576
DB0 =-0.708 calca3= 1.575
DB0 =-0.717 calca3= 1.597
DB0 =-0.726 calca3= 1.619
CCSD(T)/cc-pVTZ
All Values in MHz
semiBe =355.121calcBe = 355.385
semiBe =359.886calcBe = 360.170
semiBe =364.779calcBe =365.194
semiBe =364.786calcBe =364.978
semiBe =369.763calcBe =370.026
semiBe =374.818calcBe =375.097
Semi-Exp. vsCCSD(T)/cc-pwCVQZ
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Can we derive a semi-experimental structure from these IR-data?
Question
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Semi-Experimental Structure• Experimental data provide n different Isotopologues
n=2 for SiC3Si and n=6 for GeC3Ge• Zero-point vibrational corrections are available from CCSD(T) theory for both species.• Semi-experimental rotational constants in the equilibrium are available
semiBe = expB0 - calcDB0
• Uncertainties are in the range of 0.013 Å (for Si2C3). Not helpfull!• Fixed C-C bond length leads to precise values for the X-C distance
Methode rC-C rGe-C---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
CCSD(T)/cc-pwCVQZ 1.2893 Å 1.7683 ÅSemi-Exp. (Fixed at rC-C = 1.2893 Å) 1.7695 Å
Methode rC-C rSi-C---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
CCSD(T)/cc-pwCVQZ 1.2895 Å 1.6829 ÅSemi-Exp. (Fixed at rC-C =1.2895 Å ) 1.6850 Å
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Conclusion• Measurements of two isotopic species of Si2C3 and of six isotopic species of Ge2C3
• High resolution infrared measurements together with Coupled Cluster Theory can give quantitative information about bond lengths in X2C3 chain molecules.
• Bond length calculated at the CCSD(T)/cc-pwCVQZ level of theory investigated in this work agree within max. 2 10-3 Å (in SiC3Si and Si13C3Si).
• Relativistic calculations at the CCSD(T) / ANO-RCC-unc/SFX2c-1e level of theory indicates contractions of the order of 3 10-3 Å. (J. Gauss, Universität Mainz, Germany)
• 0
• How can non-relativistic calculations be that accurate?
C5 1.283 Å 1.290 Å SiC3Si 1.290 Å 1.682 ÅGeC3Ge 1.289 Å 1.770 Å
Values in red from CCSD(T)/cc-pwCVQZValues in black, semi-exp. values from this work
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Dipl. Phys. Volker LutterLaborastrophysikUniversität Kassel
Prof. Dr. Thomas GiesenLaborastrophysikUniversität Kassel
Dr. Sven ThorwirthLaboratory AstrophysicsUniversität zu Köln, Germany
Prof. Dr. Jürgen GaussTheoretische ChemieUniversität Mainz, Germany
Team / FundingFunding
Deutsche ForschungsgemeinschaftTH 1301/3-1 and TH 1301/3-2
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Thank you for your attention!
Volker Lutter, Laborastrophysik, Universität Kassel69th ISMS Champaign-Urbana, Illinois
Semi-Experimental StructureMethode rC-C rGe-C---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
CCSD(T)/cc-pwCVQZ 1.2893 Å 1.7683 ÅFixed rC-C =1.2893 1.7695 Å
ANO-RCC-unc 1.2913 Å 1.7704 ÅANO-RCC-unc/SFX2c-1e 1.2912 Å 1.7671 Å-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
rel. contraction 0.0001 Å 0.0033 Å