Fundamentals and Torsional Combination Bands of Two Isomers of the OCS-CO2

Complex

J. Norooz Oliaee, M. Dehghany, F. Mivehvar, Mahin Afshari, N. Moazzen-AhmadiDepartment of Physics and Astronomy, University of Calgary, Canada

A. R. W. McKellarSteacie Institute for Molecular Sciences, National Research Council of Canada

Outline

Previous works on OCS-CO2 dimer and related systems

Two distinct isomers of the OCS-CO2 complex

in OCS n1 stretching vibration

in CO2 n3 stretching vibration

Out-of-plane van der Waals mode

Summary

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Previous work: OCS-CO2

Microwave study by Novick et al (1988).

Isotopomers:OCS-CO2

OC34S-CO2

Planar with slipped near-parallel structureSulfur atom occupies the “inner” position

Carrier gas: Argon

Stewart E. Novick, R. D. Seunram and F. J. Lovas, J. Chem. Phys. 88, 687 (1988).

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Previous works on related systems: OCS-(CO2)2 trimerMicrowave study of nine isotopomers of the mixed trimer by Peebles et al (1998).

Sean A. Peebles, Robert L. Kuczkowski, J. Chem. Phys. 109, 5276 (1998).OCS-CO2-a

S-interiorOCS-CO2-bO-interior

CO2 dimer

“One expects trimers to exhibit van der Waals interactions and structures that resemble the associated dimers”

?

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OCS-CO2-bOCS-CO2-a OCS-CO2-b

CO2 dimer

?

Previous works on related systems: (OCS)2-CO2 trimerAb initio study on (OCS)2-CO2 trimer by H. Valdés and J. A. Sordo (2002).

OCS-CO2-a

Geometric parameters as computed at the MP2/cc-pVTZ level by H. Valdés et al (2002).5/13

Infrared observation of two distinct isomers of the OCS-CO2 dimer in n1 fundamental region of OCS

M. Dehghany et al, J. Chem. Phys. 130, 224310 (2009).

OCS-CO2-b

OCS-CO2-a

@ 2066.1 cm-1

@ 2055.7 cm-1

Isotopomers:OCS-13CO2

OCS-C18O2

Carrier gas: Helium

S-interior

O-interior

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Structural parameters of the two OCS-CO2 isomers

Isomer a structural parameters

RCM /Å q1 / ° q2 / °

Novick et al*

3.552(3) 68.94(30) 78.93(57)

Our Group 3.5545(10) 69.7(4) 78.7(3)

Isomer b structural parameters

RCM /Å q1/ ° q2 / °

Valdes et al†

3.913 122.45 131.05

Our Group

3.9862(10) 118.0(5) 135.8(3)

* FTMW observation by Novick et al, J. Chem. Phys. 88, 687 (1988).† ab initio calculations at the MP2/cc-pVTZ level by H. Valdés et al (2002).M. Dehghany et al, J. Chem. Phys. 130, 224310 (2009).

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Energy ordering debate: OCS-CO2-a vs. OCS-CO2-b ?

OCS-CO2-a@ 2066.1 cm-1

OCS-CO2-b@ 2055.7 cm-1

Stabilization EnergiesMP2/cc-pVTZ level (cm-1)†

OCS-CO2-a 531

OCS-CO2-b 505

† H. Valdés and J. A. Sordo, J. Phys. Chem. A 106, 3690 (2002).

Confirmed with Argon

ˣ

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Detection of both OCS-CO2 isomers in n3 fundamental region of CO2

Centered @ 2346.86 cm-1 Centered @ 2348.39 cm-1

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Out-of-plane torsional combination bands of isomers of OCS-CO2 in n3 fundamental region of CO2

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Very weak c-type bandsover 2000 averages

@ 2365.78 cm-1 @ 2364.24 cm-1

Out-of-plane torsional combination band ofOCS-CO2-a in n1 fundamental region of OCS

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@ 2084.86 cm-1

Out-of-plane torsional frequencies of the two isomers of OCS-CO2

Fundamental band Torsional bandTorsionalfrequency

OCS-CO2-aIn CO2 n3 region

2346.86 cm-1 2365.78 cm-1 18.9 cm-1

OCS-CO2-aIn OCS n1 region

2066.1 cm-1 2084.86 cm-1 18.7 cm-1

OCS-CO2-bIn CO2 n3 region

2348.39 cm-1 2364.24 cm-1 15.8 cm-1

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Summary• Fundamental spectra of two isomers of the OCS-CO2 dimer are

observed in both regions of the OCS n1 and CO2 n3 stretching vibrations.

• Intermolecular van der Waals frequencies for the out-of-plane torsion of the two isomers are measured.

• Out-of-plane torsional frequencies together with our experiment with Argon as the carrier gas confirms that isomer b is indeed the higher energy isomer.

Thank you for your attention13/13