volker lutter, laborastrophysik, universität kassel 69 th isms champaign-urbana, illinois high...

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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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


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?


Experimental Setup

IR

Nd:YAG


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)


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


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


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


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




Semi-Exp. vsCCSD(T)/cc-pwCVQZ


Can we derive a semi-experimental structure from these IR-data?

Question


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


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


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


Thank you for your attention!


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

volker lutter, laborastrophysik, universität kassel 69 th isms champaign-urbana, illinois high...

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