Pressure (GPa)

0 5 10 15 20

Ram

an s

hift

(cm

-1)

200

400

600

800

COb

ring br

1600

1800

2000

CO st

Lattice

H-SQA

Pressure (GPa)

0 5 10 15 20

Ram

an s

hift

(cm

-1)

200

400

600

800

1600

1800

2000

CO b

CO st

Lattice

D-SQA

ring br

Raman shift (cm-1)

0 200 400 600 800

Ram

an in

tens

ity (a

. u.)

Raman shift (cm-1)

1000 1200 1400 1600 1800

D-SQA

H-SQA H-SQA

D-SQALattice

C-O bC=C st

C=O st

x 2

x 10

O-H b

O-D bC-C st

ring b ring br

C=O b

Raman shift (cm-1)

1400 1500 1600 1700 1800 1900

Ram

an in

tens

ity (a

. u.)

amb.

1.5

3.1

3.8

6.2

10.3

14.8

19.3

22.2 GPa D-SQA

Raman shift (cm-1)

0 200 400 600 800 1000 1200

Ram

an in

tens

ity (a

. u.)

amb.

1.5

3.1

3.8

6.2

10.3

14.8

19.3

22.2 GPaD-SQA

Background: • Hydrogen bonding (HB) plays a key role in

determining the structure and properties of many molecular systems

• Squaric acid (SQA) is a prototypical HB molecular crystal1

• Behavior of HB not well understood under

high pressure • Previous work on SQA revealed that

structural stability of this crystal is govern by changes in the HB2

• H/D isotope effect (substitution of hydrogen with deuterium) is often used to gain insight into the HB

High Pressure Stability of Hydrogen Bonded Crystal of Squaric Acid: H/D Isotope Effect

Advised by Dr. Z. A. Dreger Institute for Shock Physics

Laura Drbohlav Clemson University

This work was supported by the DOE/NNSA Grant No. DE-NA0000970

Objectives: • Use the H/D isotope effect to further

examine the role of hydrogen bonding in structural stability of SQA crystal

• Is deuterated SQA (D-SQA) structure more stable under high pressure than H-SQA (positive Ubbelohde effect3)?

Experimental Approach: • Refluxing of H-SQA with D2O

and growing single crystals of D-SQA

Results:

Summary/Conclusions: • Performed first high pressure

measurements on D-SQA up to 22 GPa • D/H isotope effect further stabilizes the

structure of SQA under high pressure

References: 1. D. Semmingsen, F. J. Hollander, and T. P. Koetzle., J. Chem.

Phys. 66, 4410 (1977) 2. Z. A. Dreger, J. Zhou, Y. Tao, and Y.M. Gupta, unpublished. 3. A. R. Ubbelohde and K. J. Gallagher., Acta Cryst. 8, 71 (1955).

c

a

b

a

DAC

Ambient Raman Spectra of D-SQA & H-SQA

H-SQA D-SQA P = 0

P > 0

Pressure Effect on Raman Spectra of D-SQA

Raman Shift of D-SQA & H-SQA Diamond anvil cell (DAC) & Ruby Fluorescence

0

Tetragonal Molecular Twist/Rotation

H-localized

Monoclinic Molecular Symmetry Cs

D-localized

D-SQA H-SQA

~3.5 GPa

15 GPa

0.8 GPa

2 GPa

12 GPa

Monoclinic Molecular Symmetry Cs

H-localized

Tetragonal Molecular Twist/Rotation

D-localized

Tetragonal Molecular Symmetry C4h

H-delocalized

Tetragonal Molecular Symmetry Cs

H-delocalized

Tetragonal Molecular Symmetry C4h

D-delocalized

?

Raman Spectroscopy and Optical Imaging

Ruby D-SQA

2.1 GPa 4.1 GPa 8.6 GPa 14.2 GPa

Recorded Spectrum

CCD Camera

Spectrometer

Laser

DAC

O H O O D O