1. Dave Bartels Tim Marin Irek Janik
An exercise in using the Notre Dame Kinetics Database in fitting transient absorption data
Dave Bartels
Tim Marin
Irek Janik
$$$ DOE – BES Chemical Sciences, NE/NERI

2. Electron Radiolysis
This project takes advantage of radiolysis as a technique. Water radiolysis is relatively clean

3. Reaction Set for Radiolysis of Water

4. Water Properties

5. Apparatus for Supercritical Water Radiolysis Studies
Electrons can easily penetrate side of cell.

6. Reaction of OH Radical with H2
This is a real benchmark reaction-- selected at the recent water workshop. Unusual effect-- simple reaction in gas phase. Why does it slow down in liquid?
Why should this “simple” reaction slow down at higher temperature?

7. But resonance raman and epr data suggest monomer.

8. OH + CO reaction???

9. 600nm absorption of carbonate anion radical at 250C
dose

10. OH + CO reaction ???
HCO3-  CO2 + OH- ???

11. Search on carbonate radical reactions

14. 10x higher recombination
Rate constant???
CO3- + H2O2 ???

18. Relatively slow….

21. Product?? Assume 2CO2 + H2O2 + 2OH-

22. mechanism Function CarbRadiolysis(fit, tt, yw, dydt)
//OH + HCO3- --> CO3*- + H2O 0
//OH + OH --> H2O2 1
//OH + CO3*- -->HOOCO2- --> CO2 + HO2- 2
//CO3*- + H2O2/HO2-  O2- + CO3= 3
//CO3*- + CO3*- --> (too slow to matter much)
//H + OH- -> OH (via N2O) 5
//H + OH --> H2O 6
//H + CO3*- --> HCO assume same rate as H + OH
Variable tt // time value at which to calculate derivatives
Wave yw, fit // yw[0]-yw[3] containing concentrations of OH(0), CO3*-(1), H202(2),H(3)
// fit reflect rate constant of reactions 0-4
Wave dydt // wave to receive dA/dt, dB/dt etc. (output)
Wave bicarb,carb,hydrox,k_OH,k_hydrox
variable rxn0, rxn1, rxn2,rxn3,rxn4,rxn5,rxn6,rxn7,runnum
runnum=fit[6]
rxn0 = fit[0]*(bicarb[runnum]+50*carb[runnum])*yw[0] //first order scavenging(rate*bicarb conc)
rxn1 = fit[1]*yw[0]*yw[0] //second order reaction of OH--k, not 2k
rxn2 =fit[2]*yw[1]*yw[0] // OH reacts with carbonate
rxn3=fit[3]*yw[1]*yw[2] //carbonate reacts with peroxide, producing superoxide
rxn4=fit[4]*yw[1]*yw[1] // carbonate bimolecular reaction, produces peroxide
rxn5=k_hydrox[runnum]*hydrox[runnum]*yw[3] // H with hydroxide
rxn6=k_OH[runnum]*yw[3]*yw[0] // H with OH
rxn7= k_OH[runnum]*yw[3]*yw[1] // H with carbonate
dydt[0] = -rxn0 -2* rxn1 -rxn2 - rxn6 + rxn5 //OH
dydt[1] = rxn0 - rxn2 - 2*rxn3 - 2*rxn4 -rxn7 //CO3-* (rxn 3 removes two carbonate via superoxide)
dydt[2] = rxn1 + rxn2- rxn3+ rxn4//H2O2/HO2-
dydt[3] = -rxn5-rxn6-rxn7 // H atom
End

23. 4x
Assuming several shots were averaged, peroxide could build up…

24. …Yes

25. OH + bicarbonate ion

26. OH + carbonate ion