1

THE MICROWAVE SPECTRUM, STRUCTURE, AND DOUBLE PROTON EXCHANGE OF FORMIC ACID – NITRIC ACID

Becca Mackenzie

Chris Dewberry, Ken Leopold

Department of Chemistry, University of Minnesota

69th International Symposium of Molecular Spectroscopy

2

Carboxylic Acid DimersSimple carboxylic acid dimers as prototypes for larger, doubly hydrogen bonded complexes, e.g. DNA base pairs

Formic acid – Acetic acid3

Formic acid – Propiolic acid 1,2

Formic acid – Benzoic acid4

[1] Daly, A. M., Bunker, P. R., & Kukolich, S. G. (2010). JCP, 132(20), 201101. [2] Daly, A. M., Douglass, K. O., Sarkozy, L. C., Neill, J. L., Muckle, M. T., Zaleski, D. P., Pate, B. H., Kukolich, S. G. (2011). JCP, 135(15), 154304. [3] Tayler, M. C. D., Ouyang, B., & Howard, B. J. (2011). JCP, 134(5), 054316. [4] Evangelisti, L., Patricia, E., Cocinero, E. J., Castan, F., Lesarri, A., Caminati, W., & Meyer, R. (2012). JCPL, 3, 3770.[5] Feng, G., Favero, L. B., Maris, A., Vigorito, A., Caminati, W., & Meyer, R. (2012). JACS, 134, 19281–19286.

Acrylic acid dimer5

3

Double Proton Transfer

H

H

Frequency

4

Ab initio results for carboxylic acid dimers

ComplexBarrier Height

(kcal/mol)

Binding Energy

(kcal/mol)a

Hydrogen Bond

Lengths (Å)

Formic-Formic1 7.9 17.0(14.5) 1.80/1.80

Formic-Propiolic2 7.7 17.2(14.6) 1.80/1.78

Formic-Benzoic3 7.0 18.2(15.4) 1.79/1.75

Acrylic-Acrylic4 6.9 18.8 (15.8) 1.76/1.76

Nitric-Formic 9.2 14.3(11.8) 1.97/1.76

Double proton exchange observed for all

Will formic acid – nitric acid tunnel?

a. Binding energies in parentheses are counterpoise corrected MP2/6-31++G(2d,2p)

[2] Daly, A. M., Douglass, K. O., Sarkozy, L. C., Neill, J. L., Muckle, M. T., Zaleski, D. P., Pate, B. H., Kukolich, S. G. (2011). JCP, 135(15), 154304.

[3] Evangelisti, L., Patricia, E., Cocinero, E. J., Castan, F., Lesarri, A., Caminati, W., & Meyer, R. (2012). JCPL, 3, 3770.[4] Feng, G., Favero, L. B., Maris, A., Vigorito, A., Caminati, W., & Meyer, R. (2012). JACS, 134, 19281–19286.

[1] Ortlieb, M., & Havenith, M. (2007). JCP, 111, 7355.

5

Experimental

• Introduction of Sample to Cavity

• HNO3 through pulsed-nozzle

• HCOOH through continuous flow line

• Water kills the signal and creates a lot of

unwanted ones

• Started with 70% HNO3, 91% HCOOH

• Finished with 91% HNO3, 95% HCOOH

HCOOH in Ar

HNO3 in Ar

Cavity

6

Searches for the J = 2←1 Transitions

K=150 MHz

K=050 MHz

K=130 MHz

Frequency, MHz

7

Observed Lines and Fit MP2/6-311g(2d,2p) (MHz)

6154.221363.371116.11

Fit Rotational Constants (MHz)6175.461368.831121.84

Frequency, MHz

8

HCOOH - H15NO3 HCOOD - H15NO3

Evidence of Double Proton Exchange

514-413514-413

9

Spin Statistics and Relative Intensities

+

- +

3:1 ratio expected on the basis of 1H spin statistics

202-101 212-111

HCOOH-H15NO3

-

10

Evidence of Double Proton Exchange

HCOOH-HNO3

202-101

+

++

-

-

-

-

11

Single State Fits

ConstantsHCOOH-HNO3

0+ StateHCOOH-HNO3

0- StateHCOOH-H15NO3

0+ StateHCOOH-H15NO3

0- StateA (MHz) 6175.920(98) 6175.264(49) 6174.767(54) 6174.877(44)B (MHz) 1368.84012(36) 1368.84027(74) 1360.43598(44) 1360.43597(59)C (MHz) 1121.83870(36) 1121.83199(60) 1116.17782(40) 1116.17187(44)ID (amu Å2) -0.541 -0.547 -0.553 -0.54914N Χaa (MHz) -0.7885(15) -0.7872(22) - -14N Χbb-Χcc (MHz) 0.513(11) 0.440(56) - -ΔJ (kHz) 0.3249(49) 0.2897(43) 0.2912(33) 0.2875(32)ΔJK (kHz) 0.820(87) 1.261(46) 1.260(54) 1.313(53)δJ (kHz) 0.0634(49) 0.0760(95) 0.0507(35) 0.0646(42)RMS (kHz) 2 2 2 2N 39 36 18 19

12

What about the tunneling frequency?

EB

Frequency

µb= 0.21 Dµa= 2.69 D

13

Comparison of SystemsComplex Barrier Height

(kcal/mol)Binding Energy

(kcal/mol)a

Hydrogen Bond Lengths (Å)

Splitting (505-606) (MHz)b

Formic-Formic1 7.9 17.0(14.5) 1.80/1.80 ~40

Formic-Propiolic2 7.7 17.2(14.6) 1.80/1.78 2.43

Formic-Benzoic3 7.0 18.2(15.4) 1.79/1.75 0.986

Acrylic-Acrylic4 6.9 18.8 (15.8) 1.76/1.76 4.706

Nitric-Formic 9.2 14.3(11.8) 1.97/1.76 0.048

a. Binding energies in parentheses are counterpoise correctedb. Experimental values, formic-formic value calculated from IR constants MP2/6-31++G(2d,2p)

[2] Daly, A. M., Douglass, K. O., Sarkozy, L. C., Neill, J. L., Muckle, M. T., Zaleski, D. P., Pate, B. H., Kukolich, S. G. (2011). JCP, 135(15), 154304.

[3] Evangelisti, L., Patricia, E., Cocinero, E. J., Castan, F., Lesarri, A., Caminati, W., & Meyer, R. (2012). JCPL, 3, 3770.[4] Feng, G., Favero, L. B., Maris, A., Vigorito, A., Caminati, W., & Meyer, R. (2012). JACS, 134, 19281–19286.

[1] Ortlieb, M., & Havenith, M. (2007). JCP, 111, 7355.

14

Rotational Constants for Seven Isotopologues

Isotope A (MHz) B (MHz) C (MHz) 14N Χaa (MHz) 14N Χbb-Χcc

(MHz)

HCOOH-HNO3

0- State6175.264(49) 1368.84027(74) 1121.83199(60) -0.7872(22) 0.440(56)

HCOOH-HNO3

0+ State6175.920(98) 1368.84012(36) 1121.83870(36) -0.7885(15) 0.513(11)

HCOOH-H15NO3

0- State6174.877(44) 1360.43597(59) 1116.17187(44) - -

HCOOH-H15NO3

0+ State6174.767(54) 1360.43598(44) 1116.17782(40) - -

HCOOD-H15NO3 6077.493(27) 1355.55430(19) 1109.69374(17) - -

HCOOD-HNO3 6077.329(99) 1364.00473(81) 1115.3578(10) -0.811(17) 0.460(52)

H13COOH-HNO3 6172.66(15) 1347.9018(13) 1107.6852(13) -0.805(45) 0.54(25)

HCOOH-DNO3 6094.960(10) 1365.3093(11) 1116.7930(11) -0.839(11) 0.23(19)

DCOOH-HNO3 6167.29(57) 1325.6573(34) 1092.5301(41) -0.777(25) 0.344(92)

15

Structure Analysis

Leopold, K. R. (2012). JMS, 278, 27–30.

Schematic of Structure Determination

RcmFit from C rotational constants

θ1From 14N nuclear hyperfine

θ2Using Rcm and θ1

adjusted θ2 to reproduce A or B Done for all 7 isotopologues using ground state rotational constants

Using experimental moments of inertia for monomers

16

Nitric acid structure- Cox, A.P.; Ellis, M.C.; Attfield, C.J.; Ferris, A.C. (1994) JMS. 320, 91.Formic acid structure- Cazzoli, G.; Puzzarini, C.; Stopkowicz, S.; Gauss, J. (2011) AJSS. 196, 10.Winnewisser, M.; Winnewisser, B.P.; Stein, M.; Birk, M.; Wagner, G.; Winnewisser, G.; Yamada, K.M.T., Belov, S.P.; Baskakow, O.I. (2002) JMS., 216, 259.

17

Structure Results for Each IsotopologueComplex Rcm 1 2 R(H8-O5) R(O9-H4) <(O5-H8-O6) <(O3-H4-O9)

HNO3-HCOOH

3.475976 51.31 -80.40 1.6527 1.8523 166.7 172.9

H15NO3-HCOOH

3.476787 51.37 -80.42 1.6531 1.8516 166.8 172.9

H15NO3-HCOOD

3.457604 51.37 -81.77 1.6464 1.8586 166.0 173.1

HNO3-HCOOD

3.456808 51.23 -81.54 1.6472 1.8483 165.9 172.4

HNO3-H13COOH

3.484357 52.02 -80.34 1.6622 1.8435 166.9 172.3

DNO3-HCOOH

3.459116 45.24 -79.64 1.6795 1.8384 170.3 171.4

HNO3-DCOOH

3.506919 50.90 -80.60 1.6455 1.8585 170.0 172.9

Average of Max & Min Value 1.663(17) 1.849(10) 168.1(22) 172.3(9)

18

Structure of Formic Acid – Nitric AcidSeven isotopologues in total

1.663(17) Å

1.849(10) Å

168.1(22)°

172.3(9)°

D

15N

D

D

13C

19

Structure from STRFIT

R O5-O6

α C1-O5-O6

β O5-O6-N7

Kisiel, Z., (2003) JMS., 218, 58.

Structure from STRFITConverged to one of two structures depending on the

starting parameters

20

Å

Å

Å

Å

21

Summary of Structural Parameters

R(H8-O5) R(O9-H4) <(O5-H8-O6) <(O3-H4-O9)

Inertial Equations 1.663(17) 1.849(10) 168.1(22) 172.3(9)

STRFIT 1 1.67 1.84 170.0 171.5

Value from STRFIT 2 2.034 1.716 160.1 155.4

Ab initio 1.6827 1.8002 170.3 176.3

Ab initio adjusted geometry 1.680(17) 1.814(10) 172.7(22) 173.6(9)

Structure of Formic Acid – Nitric AcidPreferred structural values

1.680(17) Å

1.814(10) Å

172.7(22)°

173.6(9)°

24

Conclusions

• Like all good gophers, we tunnel

• Nitric acid – formic acid undergoes double proton transfer despite significant asymmetry in the hydrogen bonded structure.

• The splittings in the a-type spectra were two orders of magnitude smaller than those observed for related carboxylic acid dimers.

• Careful analysis of the moments of inertia yields excellent agreement with ab initio results, suggesting minimal delocalization.

25

Funding & Acknowledgements • Leopold Group

• Dr. Chris Dewberry and Dr. Brooke Timp• Lester C. and Joan M. Krogh Fellowship