Galen Sedo, Jamie L. Doran, Shenghai Wu, Kenneth R. Leopold Department of Chemistry, University of Minnesota A Microwave Determination of the Barrier to

Galen SedoGalen Sedo, Jamie L. Doran, Shenghai Wu, Kenneth R. Leopold, Jamie L. Doran, Shenghai Wu, Kenneth R. Leopold

Department of Chemistry, University of MinnesotaDepartment of Chemistry, University of Minnesota

A Microwave Determination of the A Microwave Determination of the Barrier to Internal Methyl Rotation in Barrier to Internal Methyl Rotation in

Acetic Acid MonohydrateAcetic Acid Monohydrate

Small Cluster Formation and MicrosolvationSmall Cluster Formation and Microsolvation

Types of molecular interactions and bond formation in small reactive molecular clusters

– Molecular and electronic structure changes upon complexation between water and a strong acid

Small Cluster Formation and MicrosolvationSmall Cluster Formation and Microsolvation

HH22O-HFO-HF

• Z. Kisiel, A. C. Legon, D. J. Millen, J. Mol. Struct. 1984, 112, 1-8.

HH22O-HCl & (HO-HCl & (H22O)O)22-HCl-HCl

• A. C. Legon, L. C. Willoughby, Chem. Phys. Lett. 1983, 95, 449-452.• Z. Kisiel et al., J. Phys. Chem. A 2000, 104, 6970-6978.• Z. Kisiel et al., J. Chem. Phys. 2000, 112, 5767-5776.

HH22O-HBr & (HO-HBr & (H22O)O)22-HBr-HBr

• A. C. Legon, A. P. Suckley, Chem. Phys. Lett. 1998, 150, 153-158.• Z. Kisiel et al., J. Chem. Phys. 2003, 119, 5907-5917.

HCOOH-HHCOOH-H22O, HCOOH-(HO, HCOOH-(H22O)O)22 & (HCOOH) & (HCOOH)22-H-H22OO

• D. Priem, T.-K. Ha, A. Bauder, J. Chem. Phys. 2000, 113, 169-175.

CFCF33COOH-HCOOH-H22O, CFO, CF33COOH-(HCOOH-(H22O)O)22 & CF & CF33COOH-(HCOOH-(H22O)O)33

• B. Ouyang, T. G. Starkey, B. J. Howard, J. Phys. Chem. A 2007, 111, 6165-6175.

Microwave Investigations of Acid HydratesMicrowave Investigations of Acid Hydrates

W. J. Tabor, J. Chem. Phys. 1957, 27, 974-975.• CH3COOH – Three A and E state transitions, V3 = 174 cm-1

• Observed large differences between obs and rigid

L. C. Krisher, E. Saegebarth, J. Chem. Phys. 1971, 54, 4553-4558.• CH3COOH – 39 A and 38 E state transitions, V3 = 168.2 cm-1

• Determined the barrier height with the principal axis method (PAM)

B. P. van Eijck et al., J. Mol. Spectrosc. 1981, 86, 465-479.• Determined the barrier height with the principal axis method (PAM), V3 = 168.2 cm-1

• Determined the barrier height with the internal axis method (IAM), V3 = 168.2 cm-1

Acetic Acid Monomer: CHAcetic Acid Monomer: CH33COOHCOOH

V. V. Ilyushin et al., J. Mol. Spectrosc. 2001, 205, 286-303.

V. V. Ilyushin et al., J. Mol. Spectrosc. 2003, 220, 170-186.

V. V. Ilyushin et al., J. Phys. Chem. Ref. Data 2008, 37, 97-265.• Global Fit of transitions in = 0, 1, and 2.• Determined the barrier height with the rho axis method (RAM)

V3 = 170.17408(17) cm-1 V6 = -6.47261(13) cm-1 V9 = -0.279789(70) cm-1

The Pulsed Nozzle FTMW SpectrometerThe Pulsed Nozzle FTMW Spectrometer

Mirror

Antenna

Argon bubbled through a sample of Glacial Acetic Acid: Backing

Pressure 2.25 atm

Microwave

Electronics

Computer

14732.5 14733 14733.5 14734 14734.5 14735

Frequency (MHz)Spectrum

Fabry-Perot Cavity

Diffusion Pump

Pulsed

Nozzle

Mirror

16418.0 16418.5 16419.0 16741.0 16741.5 16742.0

E State A State

111111←0←00000 CH CH33COOHCOOH

Frequency [MHz]

1,000 pulses10,000 FID’s

a V. V. Ilyushin et al., J. Mol. Spectrosc. 2001, 205, 286-303.

a

CHCH33COOHCOOH

obsD

obs-calc

obsD

obs-calcD

A-E

110←101 6088.810 0.008 6175.165 -0.013 -86.355

220←211 8560.601 0.003 9031.240 0.004 -470.639

321←312 12398.377 0.013 12508.430 -0.023 -110.053

330←321 12983.555 -0.018 14075.372 -0.019 -1091.817

211←202 12989.907 0.034 13025.271 0.004 -35.364

431←422 13381.244 -0.001 13616.999 -0.007 -235.755

541←532 16539.474 -0.011 17137.626 -0.023 -598.152

111←000 16741.492 0.031 16418.448 0.013 323.044

331←321 ---------- ---------- 8683.799 0.024 ----------

542←532 ---------- ---------- 9542.824 -0.002 ----------

221←212 ---------- ---------- 17173.064 -0.007 ----------

321←322 9944.026 0.003 10519.360 -0.020 -575.334

211←212 12453.867 0.030 12591.666 -0.018 -137.799

101←000 14803.997 0.024 14802.617 -0.026 1.380

532←533 17144.973 -0.035 17904.238 0.038 -759.265

431←432 ---------- ---------- 8534.613 0.009 ----------

414←321 ---------- ---------- 11639.023 0.002 ----------

313←220 ---------- ---------- 15152.875 -0.005 ----------

221←202 ---------- ---------- 17606.669 -0.007 ----------

A State E State

All frequencies are in MHz s = 0.025 MHz

CHCH33COOH XIAMCOOH XIAMa,ba,b Fit Fit

Rotational Constants

Centrifugal Distortion Constants

a) H.Hartwig and H.Dreizler, Z. Naturforsch 51a, 923-932 (1996).b) Available for download from the Programs for Rotational Spectroscopy website:

http://info.ifpan.edu.pl/~kisiel/prospe.htm

A 11335.888(23)

B 9478.5678(37)

C 5324.9820(31)D

J 0.00511(13)D

JK 0.01168(21)D

K -0.00223(46)d

j 0.002141(30)

V3 [cm-1] 168.558(40)Dp2J 0.3524(76)Dp2K -1.286(65)Dp2- 0.2054(28)

F0 157778(41)

Delta [º] 5.2192(77)

All values are in MHz, unless otherwise stated.

Fit Parameters


a-axis

CHCH33COOH XIAMCOOH XIAMa,ba,b Fit Fit

Internal Rotation Barrier

Inverse of the Rotor Moment of Inertia: h2/8p2I

Angle between the Internal Rotor Axisand the Principle a-axis



A 11335.888(23)

B 9478.5678(37)

C 5324.9820(31)D

J 0.00511(13)D

JK 0.01168(21)D

K -0.00223(46)d

j 0.002141(30)

V3 [cm-1] 168.558(40)Dp2J 0.3524(76)Dp2K -1.286(65)Dp2- 0.2054(28)

F0 157778(41)

Delta [º] 5.2192(77)


Fit Parameters

Internal Rotation – Overall Distortion


CHCH33COOHCOOH

obsD

obs-calc

obsD

obs-calcD

A-E

110←101 6088.810 0.008 6175.165 -0.013 -86.355

220←211 8560.601 0.003 9031.240 0.004 -470.639

321←312 12398.377 0.013 12508.430 -0.023 -110.053

330←321 12983.555 -0.018 14075.372 -0.019 -1091.817

211←202 12989.907 0.034 13025.271 0.004 -35.364

431←422 13381.244 -0.001 13616.999 -0.007 -235.755

541←532 16539.474 -0.011 17137.626 -0.023 -598.152

111←000 16741.492 0.031 16418.448 0.013 323.044

331←321 ---------- ---------- 8683.799 0.024 ----------

542←532 ---------- ---------- 9542.824 -0.002 ----------

221←212 ---------- ---------- 17173.064 -0.007 ----------

321←322 9944.026 0.003 10519.360 -0.020 -575.334

211←212 12453.867 0.030 12591.666 -0.018 -137.799

101←000 14803.997 0.024 14802.617 -0.026 1.380

532←533 17144.973 -0.035 17904.238 0.038 -759.265

431←432 ---------- ---------- 8534.613 0.009 ----------

414←321 ---------- ---------- 11639.023 0.002 ----------

313←220 ---------- ---------- 15152.875 -0.005 ----------

221←202 ---------- ---------- 17606.669 -0.007 ----------

A State E State


0

25

50

75

100

125

150

175

0 120 240 360

6-311++G(d,p)

Experimental

aug-cc-pVDZ

Møller-Plesset Second-Order Perturbation (MP2) Theory1. 6-311++G(d,p)2. 6-311++G(2df,2pd)3. aug-cc-pVDZ4. aug-cc-pVTZ

Ab InitioAb Initio Barrier Determination Barrier DeterminationCHCH33COOH MonomerCOOH Monomer

HO-C-C-H Dihedral Angle [º]HO-C-C-H Dihedral Angle

Møller-Plesset Second-Order Perturbation (MP2) Theory1. 6-311++G(d,p)2. 6-311++G(2df,2pd)3. aug-cc-pVDZ4. aug-cc-pVTZ

Experimental Monomer Barrier

S. Bell, Spectrochimica Acta Part A 2005, 61, 1471-1477

0

25

50

75

100

125

150

175

180 210 240 270 300

HO-C-C-H Dihedral Angle [º]

DE [

cm-1]

Ab InitioAb Initio Barrier Determination Barrier DeterminationCHCH33COOH MonomerCOOH Monomer

Percent Difference ~10.5%Experimental Monomer Barrier

• MP2/6-311++G(d,p)• MP2/aug-cc-pVDZ

Ab InitioAb Initio Barrier Determination Barrier DeterminationCHCH33COOH-HCOOH-H22OO

P. R. Rablen, J. W. Lockman, W. L. Jorgensen, J. Phys. Chem. A 1998, 102 3782-3797.

Q. Gao, K. T. Leung, J. Chem. Phys. 2005, 123, 074325-5.

†Counter-poise corrected geometries calculated with MP2/6-311++G(2df,2pd)

Ebind = -9.09 kcal/mol

Ebind = -5.61 kcal/mol

0

25

50

75

100

125

150

175

180 210 240 270 300

Ab InitioAb Initio Barrier Determination Barrier DeterminationCHCH33COOH-HCOOH-H22OO

Conformer A

HO-C-C-H Dihedral Angle [º]

DE [

cm-1]

Experimental Monomer Barrier

• MP2/6-311++G(d,p)• MP2/aug-cc-pVDZ


Mirror

Antenna

Argon bubbled through a sample of Glacial Acetic Acid: Backing

Pressure 2.25 atm

Microwave

Electronics

Computer

14732.5 14733 14733.5 14734 14734.5 14735


Fabry-Perot Cavity

Diffusion Pump

Pulsed

Nozzle

Mirror

Series 9PulsedSolenoidValve

Needle Adaptor

• Stainless Steal Needle Dimensions

• Argon bubbled through H2O at a rate of 1 sccm.


Mirror

Antenna

Argon bubbled through a sample of 60% Acetic Acid Solution: Backing

Pressure 2.25 atm

Microwave

Electronics

Computer

14732.5 14733 14733.5 14734 14734.5 14735


Fabry-Perot Cavity

Diffusion Pump

Pulsed

Nozzle

Mirror

Intensities x10

9405.25 9405.75 9406.25 9406.75Frequency [MHz]

E State

A State

220202←1←10101 CH CH33COOH-HCOOH-H22OO


14809.25 14809.50 14809.75 14810.00 14810.25 11326.65 11326.90 11327.15 11327.40 11327.6514809.25 14809.50 14809.75 14810.00 14810.25 11326.65 11326.90 11327.15 11327.40 11327.65

Evidence of Internal HEvidence of Internal H22O MotionO Motion

Frequency [MHz]



A StateA State


A StateA State

CHCH33COOH-HCOOH-H22OO

obs

Dobs-calc

obs

Dobs-calc

DA-E

212 ← 111 8967.222 -0.003 9294.865 0.001 -327.643

202 ← 101 9406.287 0.002 9405.581 0.008 0.706

211 ← 110 9880.767 0.016 9552.921 0.014 327.846

313 ← 212 13439.899 0.001 13747.632 -0.011 -307.733

303 ← 202 14065.226 -0.012 14062.941 -0.005 2.285

312 ← 211 14809.744 -0.013 14501.183 -0.003 308.561

414 ← 313 17900.047 0.010 ---------- ---------- ----------

110 ← 101 9055.899 0.014 10193.939 -0.004 -1138.040

211 ← 202 9530.375 0.024 10341.280 0.003 -810.905

312 ← 303 10274.858 -0.011 10779.530 0.013 -504.672

404 ← 313 11137.470 0.007 12001.990 0.003 -864.520

413 ← 404 11327.192 -0.005 11617.290 -0.007 -290.098

111 ← 000 13311.132 -0.005 11802.858 -0.008 1508.274

212 ← 101 17566.337 -0.009 16385.827 0.005 1180.510

A State E State

s = 0.012 MHzAll frequencies are in MHz

CHCH33COOH-HCOOH-H22OO

†Counter-poise corrected geometries calculated with MP2/6-311++G(2df,2pd)

a-axis

a-axis

d = 4.52º

d = 74.84º

A 11059.9422(87)B 2584.5180(22)C 2127.4831(17)D

J 0.001184(65)D

JK 0.00376(89)

V3 [cm-1] 138.477(31)Dp2J -0.0244(23)

F0 157263(30)d [º] 3.09(11)

s 0.012All values are in MHz, unless otherwise stated

Fit Parameters

9201.25 9201.75 9202.25 9202.75Frequency [MHz]

E State

A State

220202←1←10101 1313CHCH33COOH-HCOOH-H22OO

500 pulses5,000 FID’s

1313CHCH33COOH-HCOOH-H22OO

obs

Dobs-calc

obs

Dobs-calc

DA-E

212 ← 111 8781.154 -0.006 9099.482 0.002 -318.328

202 ← 101 9202.252 0.001 9201.610 0.009 0.642

211 ← 110 9655.610 0.017 9337.092 0.008 318.518

313 ← 212 13161.766 0.002 13466.844 -0.012 -305.078

303 ← 202 13763.093 -0.010 13761.018 -0.003 2.075

312 ← 211 14473.032 -0.009 14167.195 -0.002 305.837

414 ← 313 17530.920 0.009 ---------- ---------- ----------

110 ← 101 9096.978 0.014 10242.085 -0.007 -1145.107

211 ← 202 9550.327 0.022 10377.570 -0.005 -827.243

312 ← 303 10260.235 -0.008 10783.770 0.020 -523.535

404 ← 313 10639.149 -0.002 11523.131 0.006 -883.982

413 ← 404 11261.303 -0.015 11567.239 -0.001 -305.936

111 ← 000 13268.951 -0.006 11753.961 -0.009 1514.990

212 ← 101 17440.899 -0.008 16244.351 0.009 1196.548

A State E State


Fit Parameters for the Two Isotopic Fit Parameters for the Two Isotopic Forms of Acetic Acid MonohydrateForms of Acetic Acid Monohydrate

CH3COOH-H2O13CH3COOH-H2O

A 11059.9422(87) 11059.5115(86)B 2584.5180(22) 2523.3363(22)C 2127.4831(17) 2085.8595(17)D

J 0.001184(65) 0.001096(65)D

JK 0.00376(89) 0.00417(89)

V3 [cm-1] 138.477(31) 138.530(32)Dp2J -0.0244(23) -0.0222(23)

F0 157263(30) 157266(30)d [º] 3.09(11) 3.09(11)

s 0.012 0.011All values are in MHz, unless otherwise stated

HydrateMonomerhyd VV 33. D

100%

3

33

Monomer

HydrateMonomer

V

VVDifference

CH3COOH CH3COOH-H2O Dhyd. % Difference

V3 Experimental 168.558(40) cm-1 138.477(31) cm-1 30.081 cm-1 17.8 %

V3 Theory 151.444 cm-1 127.311 cm-1 24.133 cm-115.9 %

Barriers and the Change Upon Hydration

V3eff = 68.47 cm-1 Feff = 5.3 cm-1 V3eff = 68.47 cm-1 → V3

actual = 357 cm-1

G. T. Fraser, F. J. Lovas, R. D. Suenram, J. Mol. Spectrosc. 1994, 167, 231-235.

• Noted the apparent reduction in barrier height in weakly bound methanol complexes.

• Attributed the reduction to the neglected OH large amplitude motion

• Free methanol V3 = 373 cm-1 F = 27.63 cm-1

R. L. Kuczkowski et al., J. Mol. Spectrosc. 1995, 171, 248-264.

• Noted the apparent V3 decreased more in Ar-CH3OH than in other more strongly bond methanol complexes

Observed Barrier Decrease Upon Observed Barrier Decrease Upon ComplexationComplexation

F0 = 5.263(1) cm-1 Monomer

F0 = 5.246(1) cm-1 Hydrate

• 14 A State and 13 E State transitions were observed for the CH3COOH-H2O and 13CH3COOH-H2O complexes.

• The rotational constants, along with the value of the angle d, strongly suggest a structure with the acidic proton of acetic acid forming a primary hydrogen bond with the water molecule.

• The three fold barrier, V3, to internal methyl rotation was determined to decrease by 17.8 % upon formation of the monohydrate.

ConclusionsConclusions

Funding

• National Science Foundation (NSF)

• Petroleum Research Fund (PRF)

• Minnesota Supercomputing Institute (MSI)

• Dr. Kenneth Leopold

• Dr. Shenghai Wu

• Jamie L. Doran

Acknowledgements

http://www.nsf.gov/home/news.html

http://www.umn.edu/

124.7º 111.6º126.3º 111.1º

1.210 Å 1.360 Å0.968 Å

1.503 Å

1.219 Å 1.344 Å

1.504 Å

0.978 Å

R. L. Kuczkowski et al., J. Mol. Spectrosc. 1995, 171, 248-264.

• Noted the apparent V3 decreased more in Ar-CH3OH than in other more strongly bond methanol complexes

• Scaling the barrier with the F value of free Methanol corrected for the neglected secondary motion.

Complexfit

fitMonomereffactual

F

VFV 3

3

Observed Barrier Decrease Upon Observed Barrier Decrease Upon ComplexationComplexation

1

1

1

1

357

47.68

3.5

63.27

3

3

cmV

cmV

cmF

cmF

actual

fit

Complexfit

Monomereff

V3 = 373 cm-1 (Free Methanol)

CHCH33COOH XIAMCOOH XIAMa-ca-c Fit Fit


http://info.ifpan.edu.pl/~kisiel/prospe.htmc) N.Hansen, H.Mader and T.Bruhn, Molec. Phys. 97, 587-595 (1999).

Internal Rotation – Overall Rotation Distrotionc

222222

2

2222

2

22

2 2

PPPPPPPP

PPPPPP

PPP

cbcb

aaK

J

p

p

p

D

D

D

A 11335.888(23)

B 9478.5678(37)

C 5324.9820(31)D

J 0.00511(13)D

JK 0.01168(21)D

K -0.00223(46)d

j 0.002141(30)

V3 [cm-1] 168.558(40)Dp2J 0.3524(76)Dp2K -1.286(65)Dp2- 0.2054(28)

F0 157778(41)

Delta [º] 5.2192(77)


Fit Parameters


Documents

Galen Sedo, Jamie L. Doran, Shenghai Wu, Kenneth R. Leopold Department of Chemistry, University of Minnesota A Microwave Determination of the Barrier to