†) Currently at Department of Chemistry, University of Manitoba A Microwave Study of the HNO 3 -N(CH 3 ) 3 Complex Galen Sedo, † Kenneth R. Leopold Department of Chemistry, University of Minnesota

H 2 O-HX & (H 2 O) 2 -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, A. C. Legon, A. P. Suckley, Chem. Phys. Lett. 1998, 150, Z. Kisiel et al., J. Chem. Phys. 2003, 119, HCOOH-H 2 O, HCOOH-(H 2 O) 2 & (HCOOH) 2 -H 2 O D. Priem, T.-K. Ha, A. Bauder, J. Chem. Phys. 2000, 113, CF 3 COOH-H 2 O, CF 3 COOH-(H 2 O) 2 & CF 3 COOH-(H 2 O) 3 B. Ouyang, T. G. Starkey, B. J. Howard, J. Phys. Chem. A 2007, 111, Acid Ionization in Microsolvated Systems Kenneth R. Leopold Group H 3 CCOOH-H 2 O H 2 SO 4 [2008], H 2 SO 4 -H 2 O [2002, 2006] HNO 3 [2005], HNO 3 -H 2 O [1998], HNO 3 -(H 2 O) 2 [2008], HNO 3 -(H 2 O) 3 [submitted]

Acid Ionization with Increasing Binding Partner Basicity (CH 3 ) n H 3-n N-HX A. C. Legon, Chem. Soc. Rev. 1993, H 3 N-HX Determined the whole series of complexes to be best described by a neutral pair (CH 3 ) 3 N-HX Determined the ionization to progress along the series of complexes Ion pair formation is dominant in X = Br, I H 3 N-HNO 3 M. E. Ott, K. R. Leopold, J. Phys. Chem. A 1999, 103,

r AH is the “covalent” AH bond within the acid r H···B is the hydrogen bond length of the complex r HB + 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 Systems a)I. J. Kurnig, S. Scheiner, Int. J. Quantum Chem., QBS 1987, 14, 47. The parameter rho (  pt ) has been devised a to quantify proton transfer in hydrogen bonded systems.

HNO 3 -H 2 O HNO 3 -(H 2 O) 2 HNO 3 -(H 2 O) 3 Proton Transfer in Nitric Acid Systems H 3 N-HNO 3  pt = Å  pt = Å  pt = Å  pt = Å (H 2 O) 2  pt = Å ○ Theoretical Structure ● Experimental Structure

14 N Quadrupole Coupling Constants Nitrate Ion eQq = MHz a a)Adachi, A.; Kiyoyama, H.; Nakahara, M.; Masuda, Y.; Yamatera, H.; Shimizu, A.; Taniguchi, Y. J. Chem. Phys. 1989, 90, 392.

a a b b c c 14 N Quadrupole Coupling Constants Nitric Acid Hydrates eQq (NO 3 – ) ↔  cc  aa +  bb +  cc = 0  cc = ־ ½[  aa + (  bb -  cc )] a b b c c a HNO 3 -H 2 O b b c c a a HNO 3 -(H 2 O) 2 b b c c a a HNO 3 -(H 2 O) 3 H 3 N-HNO 3

Nitric Acid Ionization due to Increasing Binding Partner Basicity H 3 N-HNO 3 Both methods show an increase in HNO 3 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 3 ) 3 N-HNO 3

Fourier 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 torr)

Fourier Transform Microwave Spectrometer Pulse Nozzle (Multiple Configurations) Series 9 Pulsed Solenoid Valve Needle Adaptor

Frequency [MHz] (CH 3 ) 3 14 N-H 14 NO ← 2 21 Frequency [MHz] I1I1 I2I2 I 1 [HNO 3 ] I 2 [(CH 3 ) 3 N] (CH 3 ) 3 15 N-H 14 NO ← 2 21

I 2 [(CH 3 ) 3 N] I 1 [HNO 3 ] (CH 3 ) 3 14 N-H 14 NO ← 2 21 Frequency [MHz] (CH 3 ) 3 14 N-H 14 NO 3  (RMS) = 2.5 kHz 111 Transitions (including hyperfine) (CH 3 ) 3 15 N-H 14 NO 3  (RMS) = 4.6 kHz 37 Transitions (including hyperfine) A= (17) MHz B= (11) MHz C= (10) MHz  J = (47) MHz  JK = (24) MHz  aa =– (63) MHz  bb -  cc =–0.5810(16) MHz  aa =–0.3504(11) MHz  bb -  cc =–0.4036(28) MHz

Nitric Acid Ionization due to Increasing Binding Partner Basicity A= (17) MHz B= (11) MHz C= (10) MHz A= MHz B= MHz C= MHz 15 N Isotope Shift 202 ← 101 = MHz 15 N Isotope Shift 202 ← 101 = MHz Experimental Theory MP2/ G(2df,2pd) (CH 3 ) 3 14 N-H 14 NO 3  (RMS) = 2.5 kHz 111 Transitions (including hyperfine) (CH 3 ) 3 15 N-H 14 NO 3  (RMS) = 4.6 kHz 37 Transitions (including hyperfine)

Nitric Acid Ionization due to Increasing Binding Partner Basicity (CH 3 ) 3 N-HNO 3 HNO 3 -(H 2 O) 2  pt = Å HNO 3 -(H 2 O) 3  pt = Å HNO 3 -H 2 O  pt = Å  pt = Å H 3 N-HNO 3  pt = Å ○ Theoretical Structure ● Experimental Structure (H 2 O) 2  pt = Å

Nitric Acid Ionization due to Increasing Binding Partner Basicity  cc = - ½ [  aa + (  bb -  cc )]  cc = (57) MHz H 14 NO 3 Quadrupole Coupling Constants  aa = (11) MHz  bb –  cc = (28) MHz (CH 3 ) 3 N-HNO 3

Nitric Acid Ionization due to Increasing Binding Partner Basicity

Conclusions 1.The microwave spectrum of the nitric acid trimethylamine complex has been observed. The available experimental data are in agreement with the theoretical MP2/ G(2df,2pd) geometry. 2.Increasing the basicity of the nitric acid binding partner over the series H 2 O → NH 3 → N(CH 3 ) 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