Galen Sedo, Jamie Doran, Jane Curtis, Kenneth R. Leopold Department of Chemistry, University of...

Galen SedoGalen Sedo, Jamie Doran, Jane Curtis, Kenneth R. Leopold, Jamie Doran, Jane Curtis, Kenneth R. Leopold

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

A Microwave Study of theA Microwave Study of the

HNOHNO33-(H-(H22O)O)33 Tetramer Tetramer

Fundamentally…

• We know that for a strong acid, like HNO3, the following is true.

• The question becomes: How much water does it take to ionize one HNO3 molecule?

HNO3(g) + H2O() H3O+(aq) + NO3(aq)

H2O()

Atmosphere…

• Troposphere -- acid rain, and ammonium nitrate aerosol

-- reservoir for NOx and HOx species

• Stratosphere -- Polar Stratospheric Clouds (PSC’s)

-- polar ozone depletion

Nitric Acid HydratesNitric Acid Hydrates

(1) HNO3-H2O(2) HNO3-(H2O)2

Nitric Acid HydratesNitric Acid Hydrates

1. Canagaratna, M.; Ott, M.E.; Leopold, K.R. "The Nitric Acid - Water Complex: Microwave Spectrum, Structure, and Tunneling.“ J. Phys. Chem. A 1998, 102, 1489-1497.

2. Craddock, M. B.; Brauer, C. S.; Leopold, K. R. “Microwave Spectrum, Structure, and Internal Dynamics of the Nitric Acid Dihydrate Complex” manuscript in preparation.

• Complete experimental gas-phase structure

• Experimental 14N Quadrapole Coupling Constants

• Insight into the internal dynamics of the water sub-units

Nitric Acid Tri-hydrate, HNONitric Acid Tri-hydrate, HNO33 – (H – (H22O)O)33

1. Taesler, I.; Delaplane, R. G.; Olovsson, I. Acta Cryst. 1975, B31, 1489.

• Refined the crystal structure of Luzzati et al. (1953).

2. Ritzhaupt, G.; Devlin, J. P. J. Phys. Chem. 1991, 95, 90.

• FTIR investigations of thin crystalline films, HNO3-(H2O)n n = 1-3

3. McCurdy, P. R.; Hess, W. P.; Xantheas, S. S. J. Phys.Chem. A 2002, 106, 7628-7635.

• MP2/aug-cc-pVDZ geometry optimization of the 10-Member Ring confirmation

• Fourier transform infrared (FTIR) spectra for smaller nitric acid complexes

4. Escribano, R.; Couceiro, M.; Gomez, P. C.; Carrasco, E. Moreno, M. A.; Herrero, V. J. J. Phys. Chem. A 2003, 107, 651-661.

• B3LYP/aug-cc-pVTZ geometry optimizations of both the 10- and 8-Member Ring confirmations

• Reflection-absorption infrared (RAIR) spectra

5. Scott, J. R.; Wright, J. B. J. Phys. Chem. A 2004, 108, 10578-10585.

• MP2 and B3LYP geometry optimizations using the 6-311++G(2d,p) basis for both the 10- and 8-Member Ring confirmations

10-Member Ring: Top View

10-Member Ring: Side View



Ebinding [kcal/mol] Method/Basis Ebinding [kcal/mol]

-22.7 MP2/6-311++G(2df,2pd) *this work* -22.4(+0.3)

-31.6(+0.4) MP2/6-311++G(2d,p) Scott et al. -32.0

-29.7 B3LYP/6-311++G(2d,p) Scott et al. -29.6(+0.1)

-20.5 B3LYP/aug-cc-pVTZ Escribano et al. -19.7(+0.8)

Theoretical Structures of the HNOTheoretical Structures of the HNO33-(H-(H22O)O)33 Tetramer Tetramer

Mirror

Antenna

Argon bubbled through a sample of 90% HNO3

Backing Pressure 2–3 atm

Microwave

Electronics

Computer

14732.5 14733 14733.5 14734 14734.5 14735

Frequency (MHz)Spectrum

Fabry-Perot Cavity

Diffusion Pump

Pulsed

Nozzle

Mirror

The Pulsed Nozzle FTMW Spectrometer

Mirror

Antenna

Argon bubbled through a sample of 90% HNO3

Backing Pressure 2–3 atm

Microwave

Electronics

Computer

14732.5 14733 14733.5 14734 14734.5 14735

Frequency (MHz)Spectrum

Fabry-Perot Cavity

Diffusion Pump

Pulsed

Nozzle

Mirror

The Pulsed Nozzle FTMW Spectrometer

Series 9PulsedSolenoidValve

Needle Adaptor

• Stainless Steal Needle Dimensions ID = 0.016" Length = 0.205"

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

2,000 gas-pulses / 20,000 FID’s

Intensity = 0.09


Intensity = 0.06

H15NO3-(H2O)3

404 - 303

7246.500 7246.750 7247.000 7247.250 7247.500

Frequency [MHz]

HNOHNO33-(H-(H22O)O)33 Spectra Spectra

HNO3 Intensity ≈ 18,000

HNO3–H2O Intensity ≈ 500

HNO3–(H2O)2 Intensity ≈ 5.0

H14NO3-(H2O)3

404 -303

7273.750 7274.000 7274.250 7274.500 7274.750

Frequency [MHz]

CavityFrequency

H15NO3-(H2O)3

423 - 322

7937.750 7938.000 7938.250 7938.500 7938.750

Frequency [MHz]

HNOHNO33-(H-(H22O)O)33 Spectra Spectra


Intensity = 0.12


Intensity = 0.12

H14NO3-(H2O)3

423 - 322

7976.000 7976.250 7976.500 7976.750 7977.000

Frequency [MHz]

CavityFrequency

Nitric Acid Tri-hydrate Molecular ConstantsNitric Acid Tri-hydrate Molecular Constants

H14NO3-(H2O)3 : 74 Assigned Transitions, K-1 = 0 – 4

H15NO3-(H2O)3 : 18 Assigned Transitions, K-1 = 0 – 2

DNO3-(H2O)3 : 18 Assigned Transitions, K-1 = 0 – 2

H14NO3-(H2O)3 H15NO3-(H2O)3 DNO3-(H2O)3

A 2269.2963(32) 2268.390(12) 2246.496(16)B 1215.91162(26) 1209.0226(11) 1210.2466(19)C 798.28665(21) 795.19692(67) 792.9304(10)D

J 0.0010555(26) 0.001054(12) 0.001091(13)D

JK -0.002263(24) -0.00234(15) -0.00281(20)d

j 0.0004093(17) 0.0004102(81) 0.0004267(67)

dk 0.000831(36) 0.000831b 0.000831b

caa -0.7991(87) ---------- ----------

cbb-ccc 0.388(38) ---------- ----------k -0.432 -0.438 -0.426

b Parameter was fixed at the parent value in the final fit.

Spectroscopic Constants for HNO3-(H2O)3a

a All values, except the asymmetry parameter (k), are in MHz

Comparison of the Theoretical andComparison of the Theoretical and

Experimental ResultsExperimental Results10-Member Ring: Top View




Dexp-theo

Dexp-theo

9.346 A [MHz] -197.057-6.045 B [MHz] 16.4851.569 C [MHz] -85.123


Experimental ResultsExperimental Results

14N → 15N Isotope Shifts

10-Member Ring: Top View 8-Member Ring: Top View

Dn [MHz] Dn/nparent

Dn [MHz] Dn/nparent

Experimental 27.216 0.0037 32.805 0.003710-Member Ring 27.177 0.0037 32.836 0.00378-Member Ring 36.399 0.0046 43.014 0.0045

303 → 404 404 → 505


Experimental ResultsExperimental Results

DNO3 Isotope Shifts

10-Member Ring: Top View 8-Member Ring: Top View

Dn [MHz] Dn/nparent

Dn [MHz] Dn/nparent

Experimental 49.416 0.0068 60.305 0.006810-Member Ring 33.350 0.0046 40.643 0.00468-Member Ring 10.718 0.0014 13.161 0.0014

303 → 404 404 → 505

1414N Quadrupole Coupling ConstantsN Quadrupole Coupling ConstantsNitrate IonNitrate Ion

eQq = 0.656 MHz1

1. Adachi, A.; Kiyoyama, H.; Nakahara, M.; Masuda, Y.; Yamatera, H.; Shimizu, A.; Taniguchi, Y. J. Chem. Phys. 1989, 90, 392.

1414N Quadrupole Coupling ConstantsN Quadrupole Coupling ConstantsNitric Acid HydratesNitric Acid Hydrates

eQqNitrate Ion ↔ ccc

c

a

b

HNO3-H2O

a

b

c

HNO3-(H2O)2

a

b

c

HNO3-(H2O)3

caa + cbb + ccc = 0

ccc = ־½[caa + (cbb - ccc)]

HNO3-H2O HNO3-(H2O)2HNO3-(H2O)3

Proton Transfer in Nitric Acid SystemsProton Transfer in Nitric Acid Systems

Solvent Water Molecules vs. ccc

0.0

0.2

0.4

0.6

0 1 2 3 4

Solvent Water Molecules

ccc

Hydrates

Nitrate Ion (aq)

Dr1(OH) – Dr2(H···O)• The parameter rho () has been devisedc to quantify proton transfer in hydrogen bonded systems.

• Dr1(OH) = Stretch in O-H covalent bond relative to covalent bond in free HNO3 monomer.

• Dr2(H···O) = Stretch in hydrogen bond relative to O–H bond distance in hydronium ion (H3O+).

> 0 indicates proton transfer.

= 0 indicates equal sharing of proton.

< 0 indicates neutral pair.

Proton Transfer in HNOProton Transfer in HNO33 Complexes Complexes

c Kurnig, I. J.and Scheiner, S. Int. J. Quantum Chem., QBS 1987, 14, 47.

H

O

H

H H ONO2

r1(OH)r2(O---H)

Dr1(OH)

HNO3-H2O HNO3-(H2O)2HNO3-(H2O)3

Solvent Water Molecules vs. Proton Transfer

-1.00

-0.75

-0.50

-0.25

0.00

0 1 2 3 4

Solvent Water Molecules

Computational

Experimental


The Degree of Proton Transfer vs. ccc

0.0

0.2

0.4

0.6

-1.00 -0.75 -0.50 -0.25 0.00

c cc

Computational

Experimental

Nitrate Ion (aq)

(1) HNO3-H2O (2) HNO3-(H2O)2(3) HNO3-(H2O)3

12

3


(4) HNO3-(H2O)3

(5) HNO3-N(CH3)3(1) HNO3-H2O

The Degree of Proton Transfer vs. ccc

0.0

0.2

0.4

0.6

-1.00 -0.75 -0.50 -0.25 0.00

c cc

Computational

Experimental

Nitrate Ion (aq)

All

Linear (All)

(3) HNO3-(H2O)2(2) HNO3-NH3

12

3

4

5


ConclusionsConclusions

1. Spectra for three isotopes were observed

• Rotational Constants and the isotopic shifts indicate the spectra are those of the 10-Member Ring confirmation

2. The Potential Energy Surface of the HNO3-(H2O)2 system has been

performed using MP2/6-311++G(2pd,2df)

• The Global Minimum was found to be a 10-Member Ring

• An 8-Member Ring local minimum was also calculated

3. The degree of proton transfer was assessed using the experimental 14N Quadrupole coupling and the theoretical structure.

• Both methods suggest an increase in proton transfer when compared with the mono- and di-hydrate.

Funding

• National Science Foundation (NSF)

• Petroleum Research Fund (PRF)

• Minnesota Supercomputing Institute (MSI)

• Dr. Kenneth Leopold

Acknowledgements

• Dr. Matthew Craddock

• Dr. Carolyn Brauer

• Jamie Doran

• Jane Curtis

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

http://www.umn.edu/

Galen Sedo, Jamie Doran, Jane Curtis, Kenneth R. Leopold Department of Chemistry, University of...

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