1. Observation of the pure rotational spectra of trans and cis-HOCO Takahiro Oyama, Yoshihiro Sumiyoshi, Yasuki Endo Department of Basic Science, The University of Tokyo

2. Hydrocarbon combustion Final step of production of CO 2 Chemical reaction in the troposphere OH : Important oxidant in the atmosphere OH + CO ↔ CO 2 + H reaction The concentration of OH in the atmosphere is controlled by this reaction. CH 4  CH 3  CH 3 O 2  CH 3 OOH Ex.  CH 2 O  CO  CO 2 OH +HNO 2  HNO 3 Ex. Background OH + 2O 3  OH + 3O 2

3. Potential energy surface for the OH+CO reaction c-H · OCO(TS2) C 2v -HCO 2 -30 -20 -10 0 t-H · OCO(TS4) t-HO · CO(TS1) c-HO · CO(TS1) OH+CO H+CO 2 τ-TS Relative energy (kcal/mol) C 2v -TS OH · · CO 10 Lowest energy intermediates trans-HOCOcis-HOCO Important in understanding the reaction 2 A’

4. The most stable state trans-HOCO A metastable state cis-HOCO 6.5 kcal/mol 2.0 kcal/mol Both conformers can be observed in the gas phase. Potential energy surface for HOCO

5. cis-HOCO IR spectra in CO matrix by Jacox Theoretical studies LMR spectra and Pure rotational spectra by Sears et al. Previous studies of trans- and cis-HOCO No experimental data in the gas phase Hyperfine constants were not determined. Present study : Observation of HOCO by FTMW spectroscopy trans-HOCO

6. Pulse discharge nozzle (PDN) Vacuum chamber Sample gas CO diluted in Ar Production of HOCO H2OH2O DOCO Reservoir : H 2 O  D 2 O Diameter 10mm Stainless steel PDN Electrodes :

7. Observed spectra of cis-HOCO 22564.5 65.5 1 01 –0 00 J = 1.5–0.5 F = 2–1 0 00 2 02 1 01 1 11 1 10 (MHz) By FTMW spectroscopy 2 02 –1 01 J = 2.5–1.5 F = 3–2 a-type 45128.5 29.5 (MHz) By mmW-DR technique b-type 154027.5 28.5 1 11 –0 00 J = 1.5–0.5 F = 2–1 (MHz) By mmW-DR technique

8. Result trans-HOCO 0 00 1 11 2 02 1 01 1 10 a-type Total 22 lines 2 transitions b-type 1 transitions Watson's A-reduced Hamiltonian for doublet species H = H rot + H cd + H sr + H srcd + H hfs trans-DOCO : Total 34 lines 0 00 1 11 2 02 1 01 1 10 cis-HOCO a-type Total 25 lines 2 transitions b-type 2 transitions cis-DOCO : Total 46 lines For the analysis of observed transitions

9. Molecular constants for trans-conformer (MHz) trans-HOCOtrans-DOCOtrans-HOCO a trans-DOCO b A167767.943(13)154685.56(4)167766.20(19)154685.85(21) B 11433.43(5) 10685.97(4) 11433.49(6) 10685.830 (20) C 10686.52(5) 9981.61(4) 10686.52(6) 9981.673(20) NN 0.00883(5) 0.00730(3) 0.00909(5) 0.00707(3)  NK – 0.2961(3) – 0.17285(13) – 0.2963(3) – 0.17312(13)  aa 1550.42(4) 1431.54(3) 1548.78 1431.75  bb 9.57 a 7.11 b 9.57 7.11  cc – 27.200(7) – 24.223(4) – 27.42 – 24.2 aFaF – 6.881(6) – 0.971(2)  6.8(21) – T aa 23.322(11) 3.733(5) – – T bb – 5.33(15) – 0.13(3) – – T ab – – – –  aa – 0.064(10) – –  fit 0.0060 0.0049 b H. E. Radford et al. (1994) a T. J. Sears et al. (1993). FTMW : mmW-DR : mmW a,b = 1 : 0.1 : 0.0007 Weight for trans-conformer

10. Molecular constants for cis-conformer (MHz) cis-HOCOcis-DOCOcis-HOCOcis-DOCO A142944.929(3)110100.158(5)aFaF 82.811(7) 12.3721(19) B 11739.488(6) 11423.305(5)T aa 0.854(8) 0.176(4) C 10830.143(3) 10331.658(4)T bb 7.625(15) 1.163(7) NN 0.0090(4) 0.0092(3)T ab 4.674 a 0.7414 a  NK – 0.2961(3) – 0.152(3)  aa –– 0.121(11)  aa 1062.963(7) 814.278(14)  bb – 0.267(12)  bb 10.279(7) 10.578(10)  ab –– 0.0025 a  cc – 28.769(7) – 27.651(9)  fit 0.0085 0.0076 Constants of HOCO and DOCO were determined. Calculations : Inertial defects and r 0 structures a fixed to QCISD/cc-pVTZ

11. Inertial defect  I = 1/C – 1/B – 1/A Inertial defects HOCO  I = 0.079 uÅ 2 DOCO  I = 0.084 uÅ 2 cis-conformer HOCO  I = 0.077 uÅ 2 DOCO  I = 0.070 uÅ 2 trans-conformer trans- and cis-conformers  I small positive values Planar structure cis Planar structure trans

12. r 0 structure of trans-conformer Calc. 1 a Calc. 2 b r0cr0c r HO /Å0.9620.9630.974 r OC /Å1.3401.3421.342 b r CO /Å1.1761.1781.179 ∠ HOC/  107.8 107.5 ∠ OCO/  127.1127.0127.4 b UCCSD(T)-F12/aug-cc-pVTZ c Rotational constants : A and B for HOCO and DOCO Good agreement a RCCSD(T)/cc-pCVQZ(all) by P. Botschwina, Mol. Phys., 103, 1441 (2005)

13. b UCCSD(T)-F12/aug-cc-pVTZ r 0 structure of cis-conformer Calc. 1 a Calc. 2 b r0cr0c r HO /Å0.9710.9720.991 r OC /Å1.3281.3291.329 a r CO /Å1.1811.1831.182 ∠ HOC/  108.0108.1107.2 ∠ OCO/  130.3130.2131.1 c Rotational constants : A and B for HOCO and DOCO Good agreement a RCCSD(T)/cc-pCVQZ(all) by P. Botschwina, Mol. Phys., 103, 1441 (2005)

14. Intensities of cis- and trans-conformers 22564.522565.5 (MHz) 1 01 –0 00 J = 1.5–0.5 F = 2–1 22113.5 22114.5 (MHz) 1 01 –0 00 J = 1.5–0.5 F = 2–1 cis-HOCO trans-HOCO Intensity ratio 1.0 : 4.5 Dipole moments  a =1.3 D  a =2.5 D cis- and trans-conformers were produced nearly equally. Optimal conditionstranscis Stagnation pressure 4.5 atm 6.0 atm Discharge voltage 1.5 kV 2.0 kV

15. Comparison of the Fermi contact constants aFaF transcis HOCO– 6.881(6)82.811(7) DOCO–0.971(2)12.3721(19) Ratio7.0866.693 = 6.514 a F (Normal species) a F (Deuterated species) = HH DD Reasonable values a F (HOCO) a F (DOCO) Experimental values

16. Comparison of the Fermi contact constants Large  a F positive value The unpaired electron density on the proton Small  a F negative value by Spin polarization aFaF transcis HOCO– 6.881(6)82.811(7) Large positive value Experimental values

17. H O C O cis-HOCO O O C trans-HOCO H 2A'2A' 2A'2A' Small Information of the unpaired electron density on the proton was obtained experimentally. Large The unpaired electron orbitals of HOCO  a F : positive value  a F : negative value rhf/aug-cc-pVTZ level

18. Summary cis- and trans-conformers were produced nearly equally in the present conditions. The unpaired electron densities on the proton were different for cis- and trans-conformers. r 0 structures of both species agreed well with those of ab initio calculations. HOCO has been observed by FTMW spectroscopy.

19. Further investigations We are trying to observe this complex by FTMW spectroscopy S. Aloisio et al., J. Phys. Chem. A, 104, 404 (2000) OH+CO  HOCO*  H+CO 2 HOCO + M*  + M M=H 2 O etc. H 2 O-HOCO complex

20. 2254022580226202266022700 Predicted lines 1 01 -0 00 Observation of cis-HOCO (MHz) Observed lines Good agreement 1 01 -0 00

21. Observable lines of cis conformer 0 00 1 11 2 02 1 01 1 10 2 12 b-type 1 10 –1 01 130 GHz 1 11 –0 00 120 GHz 2 12 –1 01 141 GHz 2 02 –1 01 45 GHz2 02 –1 01 44 GHz 1 11 –0 00 152 GHz 2 12 –1 01 174 GHz 1 10 –1 01 99 GHz mmW-DR technique FTMW 4~40 GHz HOCODOCO a-type 1 01 –0 00 23 GHz1 01 –0 00 22 GHz

22. 微細、超微細相互作用 N KaKc =1 01 N KaKc =0 00 J = 0.5 J = 1.5 J = 0.5 微細構造 F = 0.0 F = 1.0 F = 2.0 F = 1.0 F = 0.0 超微細構造 HOCO : 電子スピン = 1/2 核スピン = 1/2

23. フーリエ変換マイクロ波分光法（ FTMW ） N N+1 回転遷移の観測 FTMW : 観測できる領域 ⇒ 4 ～ 40GHz それ以上の領域 ⇒ ミリ波二重共鳴 分子 FID 信号 時間 周波数 マイクロ波

24. ミリ波二重共鳴法 (mmw-DR) ミリ波 N N+1 FTMW : 4 ～ 40 GHz まで 観測領域 それ以上 : ミリ波二重共鳴法 周波数 ミリ波の周波数 二重共鳴スペクトル ピーク強度

25. ミリ波二重共鳴（ mmw-DR ） N N+1 周波数 ミリ波による コヒーレンスの崩壊 ピーク強度をモニタリング 周波数 二重共鳴スペクトル

26. Observed spectra of cis-DOCO 0 00 2 02 1 01 1 11 1 10 2 12 120625.0 26.0 1 11 –0 00 J = 1.5–0.5 F = 2.5–1.5 b-type (MHz) 43495.5 96.5 2 02 –1 01 J = 2.5–1.5 F = 3.5–2.5 a-type (MHz) 1 01 –0 00 J = 1.5–0.5 F = 2.5–1.5 (MHz) 21749.550.5

27. H O C O H O C O

28. Spin polarization O O C trans-HOCO a F = –6.8

29. cis(TS) との r 0 構造の比較 Å or °transciscis(TS) r HO 0.9740.9801.339 r OC 1.3401.3281.210 r CO 1.1811.1861.167 ∠ HOC 107.4 115.1 ∠ OCO 127.4130.9157.4 CO 2 cis 体形成 : 反応の進行に重要 ab initio OH+CO trans cis cis 体の構造 : より cis(TS) に近い cis(TS) ∠ OCO r HO OH + CO ⇔ CO 2 + H

30. Ground state 2 A' 0.972 Å 108.1° 130.2° 1.329 Å 1.183 Å StructureUCCSD(T)-F12 /aug-cc-pVTZ Molecular constants of cis-HOCO ・ Dipole moment  a =1.3 D  b =1.3 D ・ Rotational constants ab initio calculation Prediction ・ Spin-rotation constants trans-HOCO ・ Hyperfine constants QCISD/cc-pVTZ Gaussian 03 Similar procedure ・ cis-DOCO

31. Main reaction H + CO 2 OH+CO transcis Main reaction proceed through cis-conformer. Important in understanding the reaction cis(TS)

32. Molecular constants for trans-conformer (MHz) trans-HOCOtrans-DOCOtrans-HOCOtrans-DOCO A167767.943(13)154685.56(4)  aa 1550.42(4) 1431.54(3) B 11433.43(5) 10685.97(4)  bb 9.57 a 7.11 b C 10686.52(5) 9981.61(4)  cc – 27.200(7) – 24.223(4) NN 0.00883(5) 0.00730(3)aFaF – 6.881(6) – 0.971(2)  NK – 0.2961(3) – 0.17285(13)T aa 23.322(11) 3.733(5) KK 23.5904 a 16.141 b T bb – 5.33(15) – 0.13(3) NN 0.001229 a 0.00080(6)T ab – – kk 0.10(3) 0.0779 b  aa – 0.064(10) NN – 0.00000069(18) 0.00000048(9) KsKs – 0.561(5) – 0.357(6) NKNK – 0.000139 – 0.000062(2)  fit 0.0060 0.0049 b H. E. Radford et al. (1994) a T. J. Sears et al. (1993)