1. Fundamentals and Torsional Combination Bands of Two Isomers of the OCS-CO 2 Complex J. Norooz Oliaee, M. Dehghany, F. Mivehvar, Mahin Afshari, N. Moazzen-Ahmadi Department of Physics and Astronomy, University of Calgary, Canada A. R. W. McKellar Steacie Institute for Molecular Sciences, National Research Council of Canada

2. Outline Previous works on OCS-CO 2 dimer and related systems Two distinct isomers of the OCS-CO 2 complex in OCS 1 stretching vibration in CO 2 3 stretching vibration Out-of-plane van der Waals mode Summary 2/13

3. Previous work: OCS-CO 2 Microwave study by Novick et al (1988). Isotopomers: OCS-CO 2 OC 34 S-CO 2 Planar with slipped near-parallel structure Sulfur atom occupies the “inner” position Carrier gas: Argon Stewart E. Novick, R. D. Seunram and F. J. Lovas, J. Chem. Phys. 88, 687 (1988). 3/13

4. Previous works on related systems: OCS-(CO 2 ) 2 trimer Microwave 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-CO 2 -a  S-interior OCS-CO 2 -b O-interior CO 2 dimer  “One expects trimers to exhibit van der Waals interactions and structures that resemble the associated dimers” ? 4/13

5. OCS-CO 2 -b OCS-CO 2 -a  OCS-CO 2 -b CO 2 dimer  ? Previous works on related systems: (OCS) 2 -CO 2 trimer Ab initio study on (OCS) 2 -CO 2 trimer by H. Valdés and J. A. Sordo (2002). OCS-CO 2 -a Geometric parameters as computed at the MP2/cc-pVTZ level by H. Valdés et al (2002). 5/13

6. Infrared observation of two distinct isomers of the OCS-CO 2 dimer in 1 fundamental region of OCS M. Dehghany et al, J. Chem. Phys. 130, 224310 (2009). OCS-CO 2 -b OCS-CO 2 -a @ 2066.1 cm -1 @ 2055.7 cm -1 Isotopomers: OCS- 13 CO 2 OCS-C 18 O 2 Carrier gas: Helium S-interior O-interior 6/13

7. Structural parameters of the two OCS-CO 2 isomers Isomer a structural parameters R CM /Å  1 / °  2 / ° 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 R CM /Å  1 / °  2 / ° Valdes et al † 3.913122.45131.05 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). 7/13

8. Energy ordering debate: OCS-CO 2 -a vs. OCS-CO 2 -b ? Stabilization Energies MP2/cc-pVTZ level (cm -1 ) † OCS-CO 2 -a 531 OCS-CO 2 -b 505 † H. Valdés and J. A. Sordo, J. Phys. Chem. A 106, 3690 (2002). Confirmed with Argon ˣ 8/13

9. Detection of both OCS-CO 2 isomers in 3 fundamental region of CO 2 Centered @ 2346.86 cm -1 Centered @ 2348.39 cm -1 9/13

10. Out-of-plane torsional combination bands of isomers of OCS-CO 2 in 3 fundamental region of CO 2 10/13 Very weak c-type bands over 2000 averages @ 2365.78 cm -1 @ 2364.24 cm -1

11. Out-of-plane torsional combination band of OCS-CO 2 -a in 1 fundamental region of OCS 11/13 @ 2084.86 cm -1

12. Out-of-plane torsional frequencies of the two isomers of OCS-CO 2 Fundamental bandTorsional band Torsional frequency OCS-CO 2 -a In CO 2 3 region 2346.86 cm -1 2365.78 cm -1 18.9 cm -1 OCS-CO 2 -a In OCS 1 region 2066.1 cm -1 2084.86 cm -1 18.7 cm -1 OCS-CO 2 -b In CO 2 3 region 2348.39 cm -1 2364.24 cm -1 15.8 cm -1 12/13

13. Summary Fundamental spectra of two isomers of the OCS-CO 2 dimer are observed in both regions of the OCS 1 and CO 2 3 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 attention 13/13

14. Background Averaged spectrum Jet signal Background subtracted LabVIEW® screen, real-time monitoring of OCS-CO 2 -a torsional spectrum Ref. Gas signal Etalon Experimental setup: Data acquisition