1. Infrared Spectroscopic Studies of OCS Trapped in Solid Parahydrogen: Indirect Evidence of Large Amplitude Motions
Morgan E. Balabanoff and David T. Anderson
Department of Chemistry, University of Wyoming
Laramie, WY
This research is sponsored in part by the Chemistry Division of the National Science Foundation (CHE ).
Paper: TF02, 1:47 to 2:02 pm
TF. Mini-Symposium: Spectroscopy of Large Amplitude Motions

2. Carbonyl sulfide (OCS) – Infrared chromophore
n3 CO stretch (2062 cm-1)
n2 bend (520 cm-1)
n1 CS stretch (859 cm-1)
B = cm-1
TF02: SPEC LAMs David T. Anderson University of Wyoming

3. Previous studies of OCS(H2)N clusters
Superfluid helium droplets
Supersonic expansion
T = 0.15 – 0.37 K
T ≤ 1 K
Droplets: S. Grebenev, B. Sartakov, J. P. Toennies, A. Vilesov, Science 289, 1532 (2000).
Beams: J. Tang and A.R.W. McKellar, J. Chem. Phys. 116, 646 (2002).
TF02: SPEC LAMs David T. Anderson University of Wyoming

4. Vibrational frequency reflects cluster size and “structure”
hnIR
hnIR
hnIR
hnIR
v=0
v=0
v=0
v=0
monomer
N=1
N=2
N=3
TF02: SPEC LAMs David T. Anderson University of Wyoming

5. Infrared spectroscopic measurements of clusters formed in seeded jetsHe
ortho-H2
para-H2
J. Tang and A.R.W. McKellar, J. Chem. Phys. 116, 646 (2002).
J. Tang, Y. Xu, A.R.W. McKellar, W. Jäger, Science 297, 2030 (2002).
J. Tang and A.R.W. McKellar, J. Chem. Phys. 121, 3087 (2004).
TF02: SPEC LAMs David T. Anderson University of Wyoming

6. N=5 cluster is special: trend breaker
TF02: SPEC LAMs David T. Anderson University of Wyoming

7. Synthesis of parahydrogen (p-H2) enriched crystals
n-H2
cold tip
2000 ppm
Fe(OH)3
100 ppm
p-H2
infrared
beam
TF02: SPEC LAMs David T. Anderson University of Wyoming

8. Infrared spectrum of OCS in solid pH2 (CO stretch region)
[OCS]= 1 ppm
[o-H2]= 100 ppm
T = 1.89 K
as-deposited
cm-1
matrix shift = cm-1
OC32S gas-phase
n0 = cm-1
TF02: SPEC LAMs David T. Anderson University of Wyoming

9. Fine structure not just sulphur isotopomers
OC32S ?
OC34S ?
OC33S
TF02: SPEC LAMs David T. Anderson University of Wyoming

10. “Simpler” spectrum at “high” temperature
OC32S
OC34S
4.80 K
1.70 K
TF02: SPEC LAMs David T. Anderson University of Wyoming

11. Some peaks show a strange temperature dependence* *
TF02: SPEC LAMs David T. Anderson University of Wyoming

12. H2-OCS intermolecular PES; doughnut model
F. Paesani and K.B. Whaley, Mol. Phys. 104, (2006).
TF02: SPEC LAMs David T. Anderson University of Wyoming

13. Nitrous Oxide (N2O) – OCS mimic
n3 NN stretch ( cm-1)
n2 bend (588.8 cm-1)
n1 NO stretch ( cm-1)
B = cm-1
TF02: SPEC LAMs David T. Anderson University of Wyoming

14. H2-N2O intermolecular PES – 6D, 4D, 2D
L. Wang, D. Xie, R.J. Le Roy, W-P Deng, P-N. Roy, J. Chem. Phys. 139, (2002).
TF02: SPEC LAMs David T. Anderson University of Wyoming

15. Does N2O “fit” in a single substitution site?
S-M. Hu, L. Wan, J-H. Du, G. Xu, W-P. Deng, L. Wu, S-X. Tian, Y. Chen, Vib. Spec. 50, 36 (2009).
TF02: SPEC LAMs David T. Anderson University of Wyoming

16. Let’s look at this further, does N2O fit?Y X Z
TF02: SPEC LAMs David T. Anderson University of Wyoming

17. 6 minima for N2O in single substitution hcpY 5 6
theta X Z 3 4
phi 2
Theta phi Vmin(q,f) cm-1 1
146 pH2 molecules fixed
N2O com fixed
TF02: SPEC LAMs David T. Anderson University of Wyoming

18. Can we form particle(s) on a ring?Y
theta X Z
phi
N=5
TF02: SPEC LAMs David T. Anderson University of Wyoming

19. Summary
Is it possible for impurities to induce delocalized motions in the surrounding pH2 solvation shell?
Can these different solvation geometries be detected using FTIR spectroscopy and modeling?
Anomalies in the IR spectra of OCS and N2O still need to be explored further
Quantum solvation in solid pH2 is a delicate balance between zero point energy and potential energy – can lead to counterintuitive effects!
TF02: SPEC LAMs David T. Anderson University of Wyoming

20. The people who do the work and funding
Morgan E. Balabanoff
Aaron I. Strom
Wyoming Research Scholar
Fredrick M. Mutunga
This research is sponsored in part by the Chemistry Division of the US National Science Foundation through grant (CHE ). We would also like to acknowledge funds from the UW Research Office for the helium recovery system.
TF02: SPEC LAMs David T. Anderson University of Wyoming

21. 12 minima for N2O in single substitution hcpY
theta X Z
phi
Theta phi Vmin
146 pH2 molecules fixed
N2O com relaxed

22. Vibrational shifts reflect structure
- gas phase
- this work

23. Calculated “structures” for OCS(p-H2)N
monomer
N = 1
N = 2
N = 3
N = 4
N = 5
N = 6
N = 7
F. Paesani, R. E. Zillich, and K. B. Whaley, J. Chem. Phys. 119, (2003).

24. Vibrational frequency reflects cluster size and structure
hnIR
hnIR
hnIR
hnIR
v=0
v=0
v=0
v=0
monomer
N=1
N=2
N=3

25. Cluster distribution shifts with temperature
high temperature
OCS ↔ OCS(o-H2) ↔ OCS(o-H2)2 ↔ OCS(o-H2)3

26. Cluster distribution shifts with temperature
Low temperature
OCS ↔ OCS(o-H2) ↔ OCS(o-H2)2 ↔ OCS(o-H2)3

27. Ortho-H2 molecules cluster around OCS
[OCS] = 1 ppm
[o-H2] = 100 ppm
T = 1.70 K
annealed 1 2 3 5 4 7 6 8