†) Currently at Department of Chemistry, University of Manitoba A Microwave Study of the HNO 3...

††) Currently at ) Currently at Department of Chemistry, University of ManitobaDepartment of Chemistry, University of Manitoba

A Microwave Study of theA Microwave Study of the

HNOHNO33-N(CH-N(CH33))33 Complex Complex

Galen SedoGalen Sedo,,†† Kenneth R. Leopold Kenneth R. Leopold

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

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

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

• A. C. Legon, L. C. Willoughby, Chem. Phys. Lett. 1983, 95, 449-452.• 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.

Acid Ionization in Microsolvated Acid Ionization in Microsolvated SystemsSystems

Kenneth R. Leopold GroupKenneth R. Leopold Group

• H3CCOOH-H2O

• H2SO4 [2008], H2SO4-H2O [2002, 2006]

• HNO3 [2005], HNO3-H2O [1998], HNO3-(H2O)2 [2008], HNO3-(H2O)3 [submitted]

Acid Ionization with Increasing Acid Ionization with Increasing Binding Partner BasicityBinding Partner Basicity

(CH(CH33))nnHH3-n3-nN-HXN-HX

• A. C. Legon, Chem. Soc. Rev. 1993, 153-163.

HH33N-HXN-HX

• Determined the whole series of complexes to be best described by a neutral pair

(CH(CH33))33N-HXN-HX

• Determined the ionization to progress along the series of complexes

• Ion pair formation is dominant in X = Br, I

HH33N-HNON-HNO33

• M. E. Ott, K. R. Leopold, J. Phys. Chem. A 1999, 103, 1322-1328.

• rAH is the “covalent” AH bond within the acid

• rH···B is the hydrogen bond length of the complex

• rHB+ is the covalent HB bond within the free ion

pt> 0 indicates proton transfer.

pt = 0 indicates equal sharing of proton.

pt< 0 indicates neutral pair.

Proton Transfer in Hydrogen Bound SystemsProton Transfer in Hydrogen Bound Systems

a) I. J. Kurnig, S. Scheiner, Int. J. Quantum Chem., QBS 1987, 14, 47.

free

HB

complexBH

freeAH

complexAHpt rrrr

A H H B

rAHfree rH...B

rAHcomplex

The parameter rho (pt) has been deviseda to quantify proton transfer in

hydrogen bonded systems.

HNO3-H2OHNO3-(H2O)2

HNO3-(H2O)3

Proton Transfer in Nitric Acid SystemsProton Transfer in Nitric Acid Systems

H3N-HNO3pt = -0.666 Å

pt = -0.786 Åpt = -0.644 Å

pt = -0.539 Å

(H2O)2 pt = -1.04 Å

○ Theoretical Structure ● Experimental Structure

1414N Quadrupole Coupling ConstantsN Quadrupole Coupling ConstantsNitrate IonNitrate Ion

eQq = 0.656 MHza

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

a

ab

b

c

c

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

eQq (NO3–) ↔ cc

aa + bb + cc = 0

cc = ־½[aa + (bb - cc)]

a

b

b

c

c

a

HNO3-H2O

b

b

c

c

a

a

HNO3-(H2O)2

b

b

c

c

a

a

HNO3-(H2O)3 H3N-HNO3

Nitric Acid Ionization due to Nitric Acid Ionization due to Increasing Binding Partner BasicityIncreasing Binding Partner Basicity

HH33N-HNON-HNO33

• Both methods show an increase in HNO3 ionization compared to the Nitric Acid Monohydrate.

• Ionization is comparable to that of the Nitric Acid Dihydrate.

• Complex is best described as a neutral pair.

(CH(CH33))33N-HNON-HNO33

Fourier Transform Microwave SpectrometerFourier Transform Microwave Spectrometer

• Range: 3 to 18 GHz

• Typical resolution: ~5 kHz

• Pulse Nozzle (Multiple Configurations)

• Fabry-Perot Cavity (Resonance Chamber)

• 20 inch Diffusion Pump (~5 x 10-6 torr)

Fourier Transform Microwave SpectrometerFourier Transform Microwave Spectrometer

• Pulse Nozzle (Multiple Configurations)

Series 9Pulsed Solenoid Valve

Needle Adaptor

6059.25 6059.75 6060.25

6083.5 6084.0 6084.5 6085.0 6085.5 6086.0

Frequency [MHz]

(CH(CH33))331414N-HN-H1414NONO33

332222 ← 2 ← 22121

Frequency [MHz]

I1

I2

I1 [HNO3]

I1 [HNO3]

I2 [(CH3)3N]

(CH(CH33))331515N-HN-H1414NONO33

332222 ← 2 ← 22121

6083.5 6084.0 6084.5 6085.0 6085.5 6086.0

I2 [(CH3)3N]

I1 [HNO3]

(CH(CH33))331414N-HN-H1414NONO33

332222 ← 2 ← 22121

Frequency [MHz]

(CH(CH33))331414N-HN-H1414NONO33 (RMS) = 2.5 kHz(RMS) = 2.5 kHz

111 Transitions (including hyperfine)

(CH(CH33))331515N-HN-H1414NONO33 (RMS) = 4.6 kHz(RMS) = 4.6 kHz

37 Transitions (including hyperfine)

A = 3654.80(17) MHzB = 1048.85105(11) MHzC = 979.41064(10) MHzJ = 0.0001996(47) MHzJK = 0.001273(24) MHzaa = –3.28901(63) MHzbb-cc = –0.5810(16) MHzaa = –0.3504(11) MHzbb-cc = –0.4036(28) MHz

Nitric Acid Ionization due to Nitric Acid Ionization due to Increasing Binding Partner BasicityIncreasing Binding Partner Basicity

A = 3654.80(17) MHzB = 1048.85105(11) MHzC = 979.41064(10) MHz

A = 3704.100 MHzB = 1044.807 MHzC = 975.031 MHz

15N Isotope Shift

202 ← 101 = 16.661 MHz

15N Isotope Shift

202 ← 101 = 17.33 MHz

Experimental

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

(CH(CH33))331414N-HN-H1414NONO33 (RMS) = 2.5 kHz(RMS) = 2.5 kHz

111 Transitions (including hyperfine)

(CH(CH33))331515N-HN-H1414NONO33 (RMS) = 4.6 kHz(RMS) = 4.6 kHz

37 Transitions (including hyperfine)

Nitric Acid Ionization due to Nitric Acid Ionization due to Increasing Binding Partner BasicityIncreasing Binding Partner Basicity

(CH(CH33))33N-HNON-HNO33

HNO3-(H2O)2

pt = -0.644 Å

HNO3-(H2O)3

pt = -0.539 Å

HNO3-H2O

pt = -0.786 Å

pt = -0.367 Å

H3N-HNO3

pt = -0.666 Å

○ Theoretical Structure ● Experimental Structure

(H2O)2pt = -1.04 Å

Nitric Acid Ionization due to Nitric Acid Ionization due to Increasing Binding Partner BasicityIncreasing Binding Partner Basicity

cc = - ½ [aa + (bb - cc)]

cc = 0.3773(57) MHz

H14NO3 Quadrupole Coupling Constants

aa = -0.3504(11) MHz

bb – cc = -0.4036(28) MHz

(CH(CH33))33N-HNON-HNO33

Nitric Acid Ionization due to Nitric Acid Ionization due to Increasing Binding Partner BasicityIncreasing Binding Partner Basicity

ConclusionsConclusions

1. The microwave spectrum of the nitric acid trimethylamine complex

has been observed. The available experimental data are in agreement

with the theoretical MP2/6-311++G(2df,2pd) geometry.

2. Increasing the basicity of the nitric acid binding partner over the

series H2O → NH3 → N(CH3)3 promotes ionization of the acid, but

all of the 1:1 complexes are best described as neutral pairs.

Research Funding

• National Science Foundation (NSF)

• Petroleum Research Fund (PRF)

• Minnesota Supercomputing Institute (MSI)

University of Minnesota • Dr. Kenneth R. Leopold

Acknowledgements

University of Manitoba• Dr. Jennifer van Wijngaarden