1 structure of cold, mixed para-h 2 /d 2 clusters russell sliter & andrey vilesov university of...
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STRUCTURE OF COLD, MIXED PARA-H2/D2 CLUSTERS
Russell Sliter & Andrey Vilesov
University of Southern California
Department of Chemistry
OSU International Symposium on Molecular Spectroscopy
June 25, 2010
FB02
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2
He vs. H2
0 5 10 15 20 25 30 351E-3
0.01
0.1
1
10
Pre
ssu
re,
ba
r
Temperature, K
GAS
LIQUIDSOLID
TP
H2
Superfluid
Metastable superfluid
phase
Ginzburg, Sobianin, JETP Letters 15 (1972) 343
Apenko, Phys. Rev.B 60 (1999) 3052
4He H2
Boson I = 0 I = 0, 1
Mass M = 4 au M = 2 au
*Interaction εm= 11 K εm= 34 K
*Binding interaction in dimers
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Previous Work
Growth of large pH2 clusters in a seeded nozzle beam expansion
D = 1 mm Cooling and cluster growth
T0 = 15-30 KP0 = 20 atm
X% pH2 in HeKuyanov-Prozument, Kirill; Vilesov Andrey F. Physical Review Letters, 101, 205301, (2008).
• Supercooling bulk samples proven unsuccessful
• Clusters allow lower freezing point due to size effects
• Expansion w/ He allows cooling down to 0.37 K
Average Cluster Size: ~ 5*104
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4
0
2
4
0.0
0.5
1.0
350 355 360
0.0
0.5
pH2 gas seeded in He
Inte
nsity
, arb
. un.
Wavenumber, cm-1
T ≈ 1.2 K
T ≈ 10 K
T ≈ 2 K
10% pH2 in He
1% pH2 in He
0.5% pH2 in He
Free pH2
Rotational S0(0) line of pH2 clusters in He
( = 0 0, J = 2 0 )
J = 2
J = 0
Rotational CARS
• Splitting pattern depends on crystal structure
J = 2 mj = ±2, ±1, 0
Splitting in hcp crystal
Kuyanov-Prozument, Kirill; Vilesov Andrey F. Physical Review Letters, 101, 205301, (2008).
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Phase Separation in 3He/4He Mixtures
• Tc = 0.87 K• Xc(3He) = 0.67
D. O. Edwards and M. S. Pettersen, J. Low. Temp. Phys. 87, 473 (1992)
(3He)
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6()
Experimental CARS Setup Continued
PMT
L
Grating
Filters
4
1
LICARS
nozzle
T0 = 15-30 KP0 = 20 atm
X% (pH2 + D2) in He
k1 k1
k2 k3
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Vibrational CARS of pH2 in pH2/He Clusters
T = 20 K
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Vibrational CARS of pH2 in pH2/D2/He Clusters
X = 1% (H2 + D2) in He X = 8% (H2 + D2) in He
58% D2
27% D2
0% D2
85% D2
37% D2
0% D2
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Vibrational CARS of pH2 in pH2/D2 Liquid Expansion (X = 100%)
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Vibrational CARS in pH2/D2 Clusters
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In gas In solid
ν = 0
Q1(0)
Band due to vibron propagation
ΔνI = 8.7 cm-1
ΔνB = 2.7 cm-1
Δk = 0
Vibron Hopping &Vibrational shift in solid pH2
R
ν = 1
J. van Kranendonk, Solid hydrogen. Theory of the properties of solid H2, HD and D2. (1983)
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Vibron Hopping in pH2/D2 Clusters
pH2pH2
pH2pH2
pH2
pH2
pH2
pH2pH2
pH2pH2
pH2
D2
pH2
D2D2
D2D2
D2
D2
pH2
2.7 cm-1
20 %Hc
0
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Vibrational CARS of pH2 in pH2/D2 Clusters
Bulk Mixture
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Phase Separation in pH2/D2 Clusters
Randomly mixedClusters
Phase separatedClusters
D2
pH2
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Model of Phase Separation in pH2/D2 Liquids
M. Lambert, Phys. Rev. Lett. 4, 555 (1960)
• No phase separation in bulk liquid pH2/D2 mixtures
• Mixing stability based on lowering free energy
G = H – T·S
High Temperature• Entropy dominates
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Phase Separation in pH2/D2 Liquids
Modeling of phase separation
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Conclusions
• pH2/D2 solid cluster frequency shifts follow expectations observed in
bulk mixed hydrogen samples
•pH2/D2 liquid cluster vibrational Raman frequency shift saturates with increasing D2
• Phase separation observed
• Estimation of phase separation of ~ 3 K helps validate supercooled liquid clusters previously observed
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Acknowledgments
• Melody Sun• Evginy Loginov• Luis Gomez• Andrey Vilesov
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