1. Rotational spectroscopy of oxygen bearing radicals and radical complexes Yasuki Endo 2006/June/19 The University of Tokyo

2. Main interests High-resolution spectroscopy of short lived reactive species FTMW spectroscopy : Observe pure rotational transitions LIF spectroscopy : Electronic transitions Short lived species produced in a supersonic jet

3. Block diagram of the FTMW spectrometer Frequency coverage ： 4 〜 40 GHz

4. FTMW spectrometer 4–40GHz

5. Production of short lived species development of pulse discharge nozze spectrum of HC 9 N Ap. J. 371 L45 (1991)

6. Pulse Discharge Nozzle Pulse Valve Pulsed electric discharge 1.0–2.0 kV, 0.2 msec Free radicals Discharge samples containing appropriate parent molecules in Ar or Ne (0.2 – 0.5 %) to produce target species Radical compexes

7. Carbon chain species studies by FTMW spectroscopy C 3 HC 4 H*C 5 HC 6 H CCN*C 3 N*C 5 N CCO*C 4 OC 6 O C 8 O C 3 OC 5 OC 7 O C 9 O CCS*C 3 SC 4 SC 5 S HCCN* HC 3 NHC 5 NHC 7 NHC 9 N HCCOHC 3 OHC 4 O HCCS*HC 3 SHC 4 S*HC 6 S* NCCONC 3 O* NCCSNC 3 S* HNC 3 H 2 C 3 NH 2 C 4 NH 2 C 3 H CH 3 COCH 3 OO FeCOFe(CO) 3 Fe(CO) 4 MgCl *studied by LIF spectroscopy mainly motivated by radio astronomy

8. Spectroscopy of complexes Ion complexes Ar–D 3 Ar, Kr–HCO + Ar, Kr–HN 2 + Radical complexes Ar–OHSumiyoshi et al. TE06 Ne, Kr–OH Ar–SH Ne, Kr–SH H 2 O–OH Ar–HO 2

9. FTMW–mmW double resonance method W. Jaeger and M. C. L. Gerry J. Chem. Phys. 102, 3587 (1995)

10. FTMW–mmW double resonance method

11. FTMW-Optical double resonance M. Nakajima, Y. Sumiyoshi, and Y. Endo Rev. Sci. Instrum. 73, 165 (2002)

12. Principle of the double resonance method FID N+1 mm-wave K=1 N N+1 K=0 π/2 pulse N N+1 K=1 K=0 FID Population change Destruction of macroscopic polarization

13. An examlpe of the double resonance spectra Intensity (%) Frequency /MHz 100 80 60 40 20 0 786237862478625 37 ClOO 1 11 - 0 00 J = 1.5 - 0.5 F = 3 - 2 Can observe transitions in the mm-wave region

14. Merits of the double resonance spectroscopy Extend the observable frequency region b-type transitions of near prolate tops vdW modes of complexes e. g. A-SH Assignments of complicated fine and hyperfine Structures fairly common to open-shell free radicals Assignments of the species PDN system – mixture of various species two or more transitions belong to one species

15. Oxygen bearing free radicals Species with more than one ogygen atoms HOOH, HOO, FOO, O 3 X-OO, CH 3 OO, HOOOH, HOOO, … (oxygen chain species cf. carbon chain species) Oxygen bearing radical complexes H 2 O – OH, Ar – HO 2, HO 2 – H 2 O important in atmospheric chemistry

16. ClOOImportant in atmospheric chemistry Catalytic process of ozone destruction in the region ClO + ClO + M → ClO-OCl + M ClO-OCl + h → ClOO + Cl ClOO + M → Cl + O 2 + M 2 [Cl + O 3 → ClO + O 2 ] Net: 2O 3 → 3O 2 polar region: ClOx cycle does not work efficiently Halogen peroxide radicals

17. 35 ClOO iter. = 100 11688.511689.0 Frequency /MHz 79 BrOO iter. = 20 2 02 - 1 01 J = 2.5 - 1.5 F = 4 - 3 9591.59592.1 Frequency /MHz 1 01 – 0 00 J = 1.5 - 0.5 F = 3 - 2 FTMW spectra of ClOO and BrOO Discharge in a Cl 2 (Br 2 ) and O 2 mixture

18. FTMW–mmW → Molecular structure is determined experimentally ClOO Frequency /GHz 0 00 1 01 2 02 3 03 4 04 1 10 1 11 2 11 2 12 3 12 3 13 K a = 0 K a = 1 120 100 80 40 20 60 BrOO Frequency /GHz 120 100 80 40 20 60 0 00 1 01 2 02 3 03 4 04 5 05 6 06 K a = 0 Observed transitions for ClOO and BrOO

19. r e structure MRCI+Q/aVQZ (Reproduces B obs within 1%) O O Cl 1.204Å 2.081Å 115.0° O O Br 1.209Å 117.1° 2.371Å ClOO BrOO OO 1.208Å O2O2 Indicates van der Waals like nature of X ‥ O 2 Determined molecular structures

20. Anomalously weak X-O bonds X ‥ O bond becomes weaker as the size of X increases! Bond lengths of XOO and XO r XO /Å 0.5 1.0 1.5 2.0 2.5 XOO XO HFClBr FClBr Energy /kcal/mol Diss. Energy : D 0 ( XOO → X+O 2 ) 0 4 8 12 Cl+O 2 ClOO Cl+O 2 ClOO Observation of the equilibrium constant Determine dissociation energy experimentally D 0 = 4.69±0.10 kcal mol -1

21. Detection of the HO 3 radical O + HO 2  OH + O 2 H + O 3  OH + O 2 : reaction intermediate MRMP2: trans is more stable （ O. Setouchi et al.,JPC 104, 3204 (2000)) Most MO calculations

22. Production of HOOO H 2 O + O 2 / Ar HOOO discharge O 2 : 20% H 2 O : 0.15% Stagnation press. 6 atm. Large amount of O 2 is required to produce HO 3

23. Observed spectra

24. Double resonance spectra observe b-type transitions to determine its structure

25. Energy level diagram and observed transitions FTMW Double resonance 8 a-type transitions 5 b-type transitions Observe similar transitions for DOOO

26. Determined molecular constants HOOODOOO ABCABC cis66,82410,9869,43558,30410,7789,096 trans70,67610,1038,83967,7659,5028,333 exp.70,7789,9878,75067,8579,4498,299 cis, trans: ab initio calculations (MRSDCI / aug-cc-pVTZ) Molecular structure is concluded to be of trans form

27. Molecular structure Planer trans form Fairly long O-O bond: weakly bound adduct of OH + O 2 structure similar to FOO K. Suma et al. Science 308, 1885 (2005)

28. Another molecule with O-O-O bonds HOHwater, very well known HOOHhydrogen peroxyde also well known HOOOHno gas phase data matrix IR, NMR HOOOOH HOOO vs. HOOOH open shell radical closed shell molecule

29. Production of HOOOH H 2 O 2 + O 2 / Ar HOOOH discharge O 2 : 10% H 2 O 2 / H 2 O : passed through a reservoir Similar conditions to produce HOOO

30. Observed FTMW spectrum of HOOOH Only one line in 4-40 GHz No fine and hyperfine structure It is impossible to confirm this line is due to HO 3 H Double resonance spectroscopy

31. Energy level diagram and observed transitions of HOOOH

32. Determined rotational constants of HOOOH cis, trans: ab initio calculations CCSD(T) / cc-pVQZ The determined constants agree with those of trans. Trans structure : C 2 symmetry … spin statistics

33. Determined molecular structure of HOOOH O – O bond length: slightly shorter than that of HOOH (1.464 Å )

34. Large amplitude motions Molecule with 2 C 1 tops Barriers : c.a. 2000 cm -1 Almost no splittings K. Suma et al. TH08

35. Chemistry of oxygen chain molecules Halogen peroxides : very weak X – O bond HO – OO : similar to XO 2 radicals ab initio calculation: multi ref. nature quite difficult to reproduce their structure HOOOH : OO bond length shorter than H 2 O 2 single ref. ab initio calculation HOOOOH? XOOO, XOOOH …

36. Oxygen bearing radicals in atmospheric chemistry OH, HO 2 : playing important roles in atmospheric chemistry

37. Spctroscopic studies of oxygen bearing radical complexes OH:OH – H 2 O OH – CO (HOCO) HO – O 2 (HOOO) Rg – OHanalysis of large amplitude motions HO 2 :Ar – HO 2 H 2 O – HO 2 O 2 :O 2 – H 2 OFTMW spectra estimation of abundance Sizable contributions in atmospheric chemistry?

38. Rotational spectroscopy of Ar–HO 2 Prototype of HO 2 bearing complexes CH 3 OH + O 2 / Ar Ar – HO 2 disch. Both a-type and b-type transitions

39. Determined molecular structure Agrees with that of ab intio calculations Fairly large binding energy: c.a. 270 cm -1 Very small induction effects on fine and hyperfine coupling constants

40. Spectroscopic study of HO 2 –H 2 O Recombination reaction of HO 2 HO 2 + HO 2 H 2 O 2 + O 2 is enhanced if H 2 O exists (explained by the contribution of the water complex) A large number of ab initio calculations No direct spectroscopic detection in the gas phase

41. Observed sptctra of H 2 O–HO 2 Production scheme H 2 O + O 2 / Ar H 2 O – HO 2 (unlike the case of Ar – HO 2 ) Two series of spectra wth different nuclear spins

42. Predicted molecular structure 5 membered ring with two hydrogen bonds Large amplitude motions

43. Tunneling motions in H 2 O–HO 2 Tunneling motions: the groupe G 4

44. The group G 4 Character table G 4 :E(12)E*(12)* A + 1 1 1 1 A – 1 1–1–1 B – 1–1–1 1 B + 1–1 1–1 A + I H2 = 0 B + or B – I H2 = 1 A–A– with different nuclear spins G4G4

45. Observed sptctra of H 2 O–HO 2 Two series of spectra wth different nuclear spins A + stateB + /B - state

46. Observed rotational transitions Each transitons has A + and B + /B - components

47. Determined molecular structure of H 2 O–HO 2 O1 – H3 bond: 1.795 A farily short cf. 2.019 A for water dimer

48. Conclusions of the study of HO 2 –H 2 O First direct spectroscopic detection Evidences for the large amplitude motions need more sophisticated analysis Large binding energy : 9.4 kcal/mol by ab initio calculations supported by the observed centrifugal constants Provide spectroscopic data for in situ detection K. Suma et al. Science, 311, 1278 (2006) RA03

49. Members of the Laboratory K. SumaY. Sumiyoshi

50. Acknowledgement Dr. Y. Sumiyoshi Graduate students K. Suma (got PhD degree, HO 3, H 2 O 3 etc) K. Katoh H. Toyoshima C. Motoyoshi W. Funato H. Yoshikawa Support: Grant-in-aid for priority research field “ Radical chain reactions ”