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

8-Member Ring: Top View

8-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

1,000 gas-pulses / 6,000 FID’s

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

2,000 gas-pulses / 20,000 FID’s

Intensity = 0.12

1,000 gas-pulses / 6,000 FID’s

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

10-Member Ring: Side View

8-Member Ring: Top View

8-Member Ring: Side View

Dexp-theo

Dexp-theo

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

Comparison of the Theoretical andComparison of the Theoretical and

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

Comparison of the Theoretical andComparison of the Theoretical and

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

Proton Transfer in Nitric Acid SystemsProton Transfer in Nitric Acid Systems

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

Proton Transfer in Nitric Acid SystemsProton Transfer in Nitric Acid Systems

(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

Proton Transfer in Nitric Acid SystemsProton Transfer in Nitric Acid Systems

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