1

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

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

3

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

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).

5

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)

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

7

Vibrational CARS of pH2 in pH2/He Clusters

T = 20 K

8

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

9

Vibrational CARS of pH2 in pH2/D2 Liquid Expansion (X = 100%)

10

Vibrational CARS in pH2/D2 Clusters

11

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)

12

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

13

Vibrational CARS of pH2 in pH2/D2 Clusters

Bulk Mixture

14

Phase Separation in pH2/D2 Clusters

Randomly mixedClusters

Phase separatedClusters

D2

pH2

15

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

16

Phase Separation in pH2/D2 Liquids

Modeling of phase separation

17

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

18

Acknowledgments

• Melody Sun• Evginy Loginov• Luis Gomez• Andrey Vilesov

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