Faculty of Science - Department of Chemistry - Division of Physical and Analytical Chemistry

1. Faculty of Science - Department of Chemistry - Division of Physical and Analytical Chemistry Katholieke Universiteit Leuven UTOPIHAN work package 1:University of Leuven Group J. Peeters Contributions by: Luc Vereecken Thamh Lam Nguyen Jozef Peeters UTOPIHAN Meeting February 2004. Luc Vereecken

2. CH3COOH + OH Issues: - Dominant initial pathways + rate coefficient - subsequent reactions + potential competitions - final product distribution CH3COOH + OH  CH2COOH + H2O  …  CH3COO + H2O  …  CH3C(OH)2O  … PES: G2M // B3LYP-DFT/6-311++G(2df,2pd) G2M // MP2/6-311++G(2df,2pd) Acidic H : strongest bond, but strongest H-bondingAddition: highest barrier (see aldehydes, ketones)

4. Conclusions: - acidic H-abstraction has lowest barrier - methyl H-abstraction has competitive barrier - addition not relevant Problems: RRKM-ME results find 85:15 ratio, but is very sensitive to relative barrier heights: accuracy of ~ 0.2 kcal/mol required to determine reasonably accurate branching ratio (=unfeasible) Calculation of absolute rate coefficient sensitive to lowest vibrations (H-bond complex wagging)  unreliable

5. Products formed: CH3COO radical (chemically activated) will dissociatein all conditions to CH3 + CO2 (barrier 5 kcal/mol) final products CH2O + CO2 CH2COOH radical will form OCH2COOH oxy radical (NO-concentration sufficiently high) dissociates quickly to HOCO + CH2O (barrier <5 kcal/mol) HOCO + O2  CO2 + HO2 Final products for CH3COOH + OH in medium to high NO: H2O + H2CO + CO2

6. Faculty of Science - Department of Chemistry - Division of Physical and Analytical Chemistry Katholieke Universiteit Leuven UTOPIHAN work package 2:University of Leuven Group J. Peeters Contributions by: Luc Vereecken Thamh Lam Nguyen Jozef Peeters UTOPIHAN Meeting February 2004. Luc Vereecken

7. -OH-alkylperoxy radicals Alcohols + OH : H-abstraction with -OH substituent then addition of O2 rearrangement and loss of HO2 RR’CHOH + OH  RR’COH + H2O + O2  RR’COHOO + H2O RR’CO + HO2 Issues: - Can the -OH-alkylperoxy radical be thermalised - Dependence on substitution

8. Calculated at the G2M-3 method CH3CH(OH) + O2 G2M-3 = E[CCSD(T)/aug-cc-pVDZ//B3LYP/] + {E[MP2/aug-cc-pVTZ//B3LYP] -E[MP2/aug-cc-pVDZ]} + ZPE[B3LYP/cc-pVTZ] 0.0 Erel (kcal/mol) CH3CHO + HOO -25.6 -23.4 TS -32.2 CH3CHO…HOO -35.5 pp -35.8 mm -35.9 pt -36.5 mt -37.0 pm -38.1 mp CH3CH(OH)OO

9.  In atmospheric conditions: - stabilization negligible - no subsequent acid formation Stabilization Barrier height H2COHCH3HCOH(CH3)2COH < 0.002 %< 0.03 %< 0.03 % 13.5 kcal mol-112.5 kcal mol-111.2 kcal mol-1

10.  Reverse reaction : RRC=O + HO2: - Thermal redissociation very fast - [RRCOHOO] low, even at 210 K reaction of RRCOHOO with NO/HO2 is not an important sink for ketones/aldehydes in UTLS Thermal dissociation (300K) Reverse reaction } H2COCH3HCO(CH3)2CO 200 s-12000 s-125000 s-1  1013 cm3 molec-1 s-1

11. Radicals with -peroxy substituents Geometries Energies Localization B3LYP-DFTBH&H-DFTMP2 Single pointIRCMAX CCSD(T) RR’COOH : with R and/or R’ = H, CH3 Low levels of theory give fake minimaDisappear at higher levels of theory -OOH substituted radicals don’t exist. RR’COOH  RR’C=O + OH Electron strongly delocalized Still not stable (B3LYP-DFT)Barrier to dissociation <1.3 kcal/mol (BH&H-DFT)

12. RR’COOR” with R,R’ = H,CH3 and R”=CH3 B3LYP-DFT finds minimum (e.g. CH3CHOOCH3)Minimum disappears with ZPE-correction (-0.5 kcal/mol)  -alkylperoxy alkyl radicals are also unstable CCSD(T) confirmation in progress RR’COOR”  RR’C=O + R”O Calculations almost finished, publication being written