1. Dynamics in Solid Hydrogen below 4 K David T. Anderson Department of Chemistry, University of Wyoming Laramie, WY 82071-3838 danderso@uwyo.edu 60 th International Symposium on Molecular Spectroscopy

2. Outline Growing H 2 clusters in the condensed phase Impurity induced H 2 nuclear spin conversion Chemical reaction dynamics at low temperature

3. Preferential formation of ortho-H 2 -HF in slit jet spectra j=0 H2H2 H F H F H H j=1 D 0 = 29.71 cm -1 D 0 = 48.28 cm -1 Expt: C. M. Lovejoy, D. D. Nelson, Jr., and D. J. Nesbitt, JCP 87, 5621 (1987). Theory: D. C. Clary and P. J. Knowles, JCP 93, 6334 (1990). para-H 2 -HFortho-H 2 -HF A. R. W. McKellar is studying X(H 2 ) n clusters in the gas-phase

4. 13.8 K 32.98 K Grow H 2 crystals via rapid vapor deposition S. Tam and M. E. Fajardo, Rev. Sci. Instrumen. 70, 1926 (1999). 15 K2 K

5. Growing solid parahydrogen crystals S. Tam and M. E. Fajardo, Rev. Sci. Instrumen. 70, 1926 (1999). room temperature dopant (e.g., CH 3 F) vacuum shroud radiation shield optical substrate T = 2.4 K IR beam atmosphere vacuum cryostat cold tip catalytic converter Fe(OH) 3

6. Experimental set-up IR ortho/para converter p-H 2 gas turbo pump dopant Specifications sample-in-a-vacuum liquid helium cryostat (1.7 – 5.0 K) variable temperature ortho/para converter (10 - 80 K) 180 l s -1 turbo pump (<10 -4 torr during deposition) IR diagnostics – Bruker IFS120 (0.008 cm -1 )

7. Studying CH 3 F(ortho-H 2 ) n clusters in solid parahydrogen para-H 2 London dispersion weaker ortho-H 2 dipole-quadrupole stronger binding energies that differ by 5 cm -1 (60 J mol -1 ) are significant at T ≤ 4 K

8. CH 3 F(ortho-H 2 ) n clusters in solid hydrogen 100 2200 7200 17000 [ortho] /ppm K. Yoshioka and D.T. Anderson, JCP 119, 4731(2003). [CH 3 F] = 0.5 - 5 ppm n =

9. ortho-H 2 clusters around CH 3 F H 3 CF para-H 2 ortho-H 2 n = 1 n = 2n = 3 n = 0

10. as-deposited 1 st annealing 1 st annealing increases cluster size 2.5 K 4.4 K 7 ppm CH 3 F 5.7% ortho-H 2

11. Takes time to approach low temperature cluster equilibrium 4.4 K → 1.8 K 0 hr 1 hr 2 hr 3 hr difference at 1.8 K spectrum is still changing after 3 hours!

12. ortho-H 2 can move by a process called “rotational diffusion” after before this process can be facile even at T = 2 K!!

13. 4.3 K 1.8 K ? =9 ≥12 Reversibly grow larger clusters at low temperature 4.3 K 1.8 K

14. Reversibly “boil-off” outer ortho-H 2 molecules T = 1.8 KT = 4.4 K

15. Low temperature irreversible process – CH 3 F induced H 2 nuclear spin conversion 1 H½ 2.79285 19 F½ 2.62887 atomspinnuclear magnetic moment

16. CH 3 F catalyzed ortho-H 2 → para-H 2 conversion minutes

17. Summary ortho-H 2 molecules preferentially cluster around polar impurities even in solid molecular hydrogen solid molecular hydrogen is dynamic at liquid helium temperatures CH 3 X catalyzes H 2 nuclear spin conversion while OCS or N 2 O do not

18. The usual suspects (2004) Kazuki Yoshioka Subrahmanyam Garimella Paul Raston Adam Oman Britney Lorenz Becker Funding The American Chemical Society Research Corporation Department of Defense (AFOSR) The National Science Foundation Collaborators Mario E. Fajardo, Eglin AFB, Florida R. J. Hinde, University of Tennessee

19. annealed, 1.83 K annealed, 1.67 K N 2 O(ortho-H 2 ) n N 2 O(ortho-D 2 ) n Assigning X(H 2 ) n cluster spectra in SMH