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

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

Reaction Set for Radiolysis of Water

Water Properties

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

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?

But resonance raman and epr data suggest monomer.

OH + CO3- reaction???

600nm absorption of carbonate anion radical at 250C dose

OH + CO3- reaction ??? HCO3-  CO2 + OH- ???

Search on carbonate radical reactions

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

Relatively slow….

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

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*- --> 4 (too slow to matter much) //H + OH- -> OH (via N2O) 5 //H + OH --> H2O 6 //H + CO3*- --> HCO3- 7 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

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

…Yes

OH + bicarbonate ion

OH + carbonate ion