Adsorption of acetone on iceAdsorption of acetone on ice:FTIR ReflectionFTIR Reflection--Absorption Spectroscopy,Absorption Spectroscopy,

Molecular Dynamics Molecular Dynamics and Quantum Mechanical Studiesand Quantum Mechanical Studies

WHY ?WHY ?

•• Implication to atmospheric and biospheric chemistryImplication to atmospheric and biospheric chemistry1.1.Chemistry (heterogeneous) of oxygenated hydrocarbons in the Chemistry (heterogeneous) of oxygenated hydrocarbons in the troposphere and ice/marine boundary layer.troposphere and ice/marine boundary layer.2. Ozone depletion 2. Ozone depletion

•• Chemical events on the surfaces of ice/hydrate Chemical events on the surfaces of ice/hydrate particles particles –– adsorption, penetration, transformations adsorption, penetration, transformations

OverviewOverview

Acetone on iceAcetone on ice

•• NonNon--crystalline versus polycrystallinecrystalline versus polycrystalline•• Modeling of nearModeling of near--surface regionsurface region•• OH dangling bondsOH dangling bonds

IceIce

•• Adsorption sites: mono and doubly coordinated statesAdsorption sites: mono and doubly coordinated states•• Hydrogen bondingHydrogen bonding•• Solid acetone phaseSolid acetone phase

Schematic partial phase diagram of water

320

273

170135

Liquid water

IhIh IVV

II

III

LDALDA

Ic

HDAHDA

HDAHDA

T (K)

220

120 VI

70

IX20

0 2 4 6 8 10 12Pressure ( kbar )

4800 4400 4000 3600 3200 2800 2400 2000 1600 1200

0.0

0.2 317033053390

2230 1640 50 nm

Wavenumber (cm-1)

0.0

0.22245 1620

3120

31853340

30603470

550 nm

0.0

0.21620

22552520

3075

3175

3480 3340

3780

(a) pc-ice, 160 K

1000 nm

0.0

0.2

Abso

rban

ce 165022353315

3405

50 nm

0.0

0.216552230

309031453495

550 nm

0.0

0.216502245

2520

31053730

3350

3505

(b) nc-ice, 131 K

1000 nm

3800 3600 3400 3200 3000 2800

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07Transformation ofnc-ice to pc-ice

3153 cm-1

3240 cm-1

3383 cm-1 3307 cm-1

3314 cm-1

3394 cm-1

Fresnel, pc-ice, 3 nm

159 K, 40 min

165 K, 400 sec

166 K

157 K

Fresnel, nc-ice, 3 nm

nc-ice, 135 K, ~ 3 nm

4000 3600 3200 2800

0.000

0.004

0.008

0.012

0.016

0.020

0.024

Wavenumber, cm-1

Absorbance

3153 cm-1

3420 cm-1

3326 cm-1

3235 cm-1

6000 5000 4000 3000 2000 1000

0.0

0.5 π σ 16302235

(d)

2910

4220

Inte

grat

ed A

bsor

banc

e O

H d

angl

ing

bond

s

750 nm

Abs

orba

nce

Wavenumber (cm-1)

0.0

0.5 36901630

2235

(c)

25301000 nm

0.0

0.5 16302235

(b)

1950

4345

3575Fresnelpc-ice1400 nm

0 200 400 800 1200 1600 2000

0

2

4

x 1x 10

π σ non-polarized

(a)

Film Thickness (nm)

C=O stretch (ν3 A1) 1731 cm-1

Selected vibration modes of free acetone molecule

C-C asym. stretch (ν17 B1) 1215 cm-1

CH3 sym. deformation (ν16 B1) 1363 cm-1

1720 1680 1440 1360 1280 1200

0.000

0.002

0.004

0.008

0.0091373cm-1 1238 cm-11711 cm-1

1703 cm-1

Soak 200 sec

240 sec

80 sec

40 sec

20 sec

Ac/nc-ice, < 5nmT= 135 K, P= 1 x 10-8 Torr

x 3

x 3

Wavenumber, cm-14000 3600 3200 2800

0.000

0.004

0.008

0.012

0.016

3145 cm-13280 cm-1

3250 cm-1

3696 cm-1

Ac/nc-iceT= 135 K, P= 1 x 10-8 Torr

x 3

x 3

3012 cm-1

0.000

0.004

0.02

0.04

1362 cm-11372 cm-1

1366 cm-1

1708 cm-1

1226 cm-1

1240 cm-1

1718 cm-1

1701 cm-1

70 sec

20 sec

Ac/CuT= 145 K, P= 1 x 10-6 Torr

Ac/pc-iceT= 160 K, P= 1 x 10-7 Torr

x 3

x 3

x 3

0.000

0.002

3145 cm-1

3694 cm-1

Ac/pc-iceT= 160 K, P= 1 x 10-7 Torr

x 3

1740 1730 1720 1710 1700 1690 1680 1670

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08(b)

DCB

A

1708

1715

17151699

1699

1709

1708

1707

A1 ν 3nc-iceP = 1 x 10-6 Torr

Abso

rban

ce

Wavenumber (cm-1)1450 1400 1350 1300 1250 1150 1100

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035(b)

D. 625 sec

C. 525 sec

B. 375 sec

A. 125 sec

nc-iceP = 1 x 10-6 Torr

B2 ν 22

B1 ν 17

1094

1097

1237

1237

1240

1227

1227

1237 1240

1372

1423

1372

B1 ν 16

A1 ν 5

1367

1367

13681358

1346

1351B2 ν 21

A1 ν 4

B1 ν 15

1404

1438

1419

-0.002

0.000

0.002

0.004

0.006

(a)

J

I

B2 ν 22

B1 ν 17

A1 ν 5

B1 ν 16

B2 ν 21

A1 ν 4

1433

13661417

1417

1097

1234

1234

13461351

1366

pc-iceP = 5 x 10-5 Torr

0.005

0.010

0.015

0.020

0.025

0.030

0.035(a)

x 3

x 3

x 3

x 3

J. 40 sec

I. 30 sec

H. 20 sec

G. 10 sec

E. 30 sec

F. 840 sec

1699

1699

1699

1716

1716

1710

1710

1712

1712

1712

1700

1700

A1 ν 3

pc-iceP = 5 x 10-5 Torr

P = 1 x 10-6 Torr

1760 1720 1680 1500 1400 1300 1200

0.000

0.004

0.008

0.012

0.016

0.020

0.024

0.028

0.032Ab

sorb

ance

120 sec

100 sec

80 sec

60 sec

40 sec

20 sec

1442 cm-1

1420 cm-1

1235cm-1

1226 cm-1

1241 cm-1

1367 cm-1

1356 cm-1

1374 cm-1

1716 cm-1

1711 cm-1

1699 cm-1

4000 3600 3200

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

Wavenumber, cm-1

Ac/nc-ice, 60 nmT= 128 K, P= 1 x 10-7 Torr

3700 cm-1 3005 cm-1

Stable orthorombic low-temperature phase of acetone. Pbca; a = 8.873 Å, b = 8.000 Å, c = 22.027 Å.

ab

c

Pbca Acetone phase. Perpendicular motifPbca Acetone phase. Perpendicular motif

a

b

c

Pbca Acetone phase. Pbca Acetone phase. Antiparallel Antiparallel and perpendicular motifsand perpendicular motifs

a

bc

1720 1700 1400 1300 1200 1100

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6(b.II)

1714

1716

17091707

17051699

1435

1419 1403

1372

13511346

1239

1097

x10x10

x100

x 100

x 10 x 30 x 30x 30

Solid Ac. T = 130 KP= 1 x 10-6 Torr, 10 minπ-polarization

Wavenumber (cm-1)3000 2900 2800

-2

-1

0

1

2

(b.I)

2969

2921

3004

0

2

4

6

8

10

12Solid Ac. T = 130 Kσ -polarization

(a.II)

D

C

B

A1714

1714

17051699

1706

1706 170516991714

17051704

1699

1713

1705

1702

1698

Abso

rban

ce

-4.5

-3.0

-1.5

0.0

1.5

3.0

4.5

6.0(a.III)

D

A

1437

1417

14031362

13501345

1436

14171403

13761364

13501345

1242

1235

1226

1241 1235

1226

1096

1096

x 5

0

2

4

6

8(a.I)

D

C

B

A

29993003

2970 2921

29702922

29993003

30032999

29692921

x 10

x 10

x 5