Role of Quantum Chemistry in Atmospheric Chemical Mechanism Development

Transcription

1 Role of Quantum Chemistry in Atmospheric Chemical Mechanism Development Renyi Zhang and Jun Zhao Department of Atmospheric Sciences Texas A&M University College Station, TX Presented at the international Conference on Atmospheric Chemical Mechanisms, December 8, 2006, Davis, CA

2 Theoretical P Etot Ri ( E R Quantum Chemical Calculations DFT, Ab initio (MP2, CCSD(T), Multiconfiguration CASSCF, etc Kinetic Calculations Transition Station Theory (TST) or Canonical Variational Transition State Theory (cvtst) RRKM/Master Equation Formalism dni = Rfi ωni Pijn j krini dt j r Separate Statistical Ensemble (SSE) Theory ) = E tot 0 {( N i N Experimental Ri Ri ( E ( E R R ) )) Etot ER 0 [ E tot E R 0 N N2 [ N ( E N2 N2 ( E ) N N2 rel mot ) N ( E rel mot tot ( E tot E R E Ion Drift-Chemical Ionization Mass Spectrometry (ID-CIMS) for kinetics and mechanism of intermediate radical species and product yields R E N2 E N2 )] de )] de N2 N2 } de R

3 W Lei et al, Theoretical study of H- 2 -isoprene peroxy radicals, J Phys Chem, 105, 471 (2001) 2 (A) 034 H H H (I) 056 (II) 002 H H H (E) 022 (B) 002 Isoprene H (III) 005 H (C) 005 H (IV) 037 H (D) 029 H (F) 008

4 W Lei and R Zhang, Theoretical study of hydroxy-isoprene alkoxy radicals and their decomposition pathways, J Phys Chem, 105, 3808 (2001) H 15 H H 2 C H II I CH 3 H =CH = H H (Ia) (Ib) (Ic) (II) Energy (kcal mol -1 ) H H CH 3 H (Ia) (Ib) III H H IV H V H VI H H = = H H = H (III) (IVa) (IVb) (V) (VI) Energy (kcal mol -1 ) H H H (IVb) (IVa) -10

5 J Zhao et al, xidation mechanism of δ-hydroxyisoprene alkoxy radicals: hydrogen abstraction versus 1,5 H-shift, Chem Phys Lett 369, 204 (2003) 2 H (A1) H 2 H (A) H H (A2) 2 H (B1) H 2 H (B) H H (B2)

6 D Zhang et al, Hydroxyperoxy nitrites and nitrates from H initiated reactions of isoprene, J Am Chem Soc, 124, 9600 (2002) H C 5 H 8 2 R 2 N RN* Dissociation or isomerization R N 2 3 production V R 2 N IV I Stabilization RN RN 2 20 N x removal Energy (kcal/mol) RN R N 2 V IV I Rate (s -1 ) Relative Probability RN 2 I V IV Energy (kcal mol -1 ) 00

7 E Fortner et al, Development of ion drift-chemical ionization mass spectrometry, Anal Chem 76, 5436 (2004) Radical Source/ Carrier Gas Pump Ion Source Pump Reactants Flow Tube Drift Tube Turbo Pump A ( or -) X X ( or -) others, k [X ] = k [A][X] dt dt = l/u [X fr ] = P/ p [X] A = H 3, Proton-transfer reaction MS, PTR-MS k determined using the average-dipole-orientation (AD) theory

8 R Zhang et al, Kinetic studies of H-initiated reactions of isoprene, J Geophys Res, 105, (2000) H C 5 H 8 C 5 H 8 H, k = cm 3 molecule -1 s -1 H - C 5 H 8 H

9 D Zhang et al, Experimental study of N reaction with hydroxyalkyl peroxy radicals from H-initiated reaction of isoprene, J Phys Chem 107, (2003) C 5 H 8 H 2 N C 5 H 8 H N 2, k = 9 x cm 3 molecule -1 s H - 6 Signal (arb units) 6 4 C 5 H 8 H 2 - Signal (arb units) 4 C 5 H 8 H 2 - N Time (s) Time (s)

10 J Zhao et al, Quantification of hydroxycarbonyls from H-isoprene reactions, J Am Chem Soc 126, 2686 (2004) 2 H (I_ Z) 1,5 H-Shift H H (a) H (A, MW=100) Dissociation H H H (D, MW=86) H H 1,5 H-Shift H (II_ Z) 1,5 H-Shift (I_ E) H H H H 2 (a) H H H (E, MW=86) H (a) Dissociation H (B, MW=100) Dissociation H H H H (F, MW=86) Sig (cps) m/z H H 2 (II_ E) (C, MW=100)

11 Zhao et al, J Am Chem Soc 126, 2686 (2004) 2000 Yield =193 % (k iso /k car )* S car (cps) S iso (cps) Yield =33 % (k iso /k car )* S Car (cps) Yield = 55% (k iso /k car )* S car (cps) S iso (cps) S iso (cps)

12 J Fan and R Zhang, Atmospheric oxidation mechanism of isoprene, Environ Chem 1, (2004) rganic Nitrate N 008 H H H (ISA) H (ISB) H (ISC) H (ISD) 092 H (IS H 2 A) 2 rganic Nitrate 060 N H H 092 (IS 2 G) H 020 H N rganic Nitrate 008 H 2 H (IS E) H H H H 040 N rganic Nitrate H 092 H 2 (IS 2 C) H H N rganic Nitrate 008 H (IS 2 D) H N 008 (IS 2 H) 092 N 008 H 092 (IS 2 F) rganic Nitrate H rganic Nitrate 2 2 H H H H H 2 H 2

13 Fan and Zhang, Environ Chem 1, (2004) C H 3 H H C H 3 CH 3 H H H H H CH 3 CH 3 (CI1) (CI2) (CI3) (CI1) (CI4) (CI5) Stabilization N, etc Stabilization H CH 2 3 H C H 3 C H Stabilization CH 3 Stabilization H H Stabilization N, etc N, etc N, etc H 2 N, etc H 2 HCH H 2 H HCH MVK MVK MVK MVK MACR =C(CH 3 )CH MACR MACR =C(CH 3 )CH MACR H 2 H 2 H H

14 Fan and Zhang, Environ Chem 1, (2004) N 3 (ISN1) N 3 N CH 3 N 3 N N 3 N N 3 N 3 N 3 N (ISN5) N (ISN8) N (ISN3) N 3 N 3 N 3 N 3 CH 2 N 2 N N 3 2 N 3 (ISN4) N CH N 2 2 N 3 N 3 N 3 (ISN2) 2 N (ISN6) 0074 N N N N 3 N 3 N 3 N 2 N 3 (ISN7) N 3

15 Fan and Zhang, Environ Chem 1, (2004) Concentration (molecule cm -3 ) 30E12 20E12 10E12 00E00 (a) New PSM Time (Days) CM MM21 Concentration (molecule cm -3 ) 80E11 (a) 60E11 40E11 20E11 New PSM CM MM Time (Days) Concentrations (molecule cm -3 ) 16E07 12E07 80E06 40E06 00E00 (b) New PSM CM MM Time (Days) Concentrations (molecule cm -3 ) 30E06 20E06 10E06 00E00 (b) New PSM CM MM Time (Days) Comparisons of 3 (a) and H (b) concentrations at high (right) and low (left) N x conditions predicted by the various mechanisms

16 Conclusions Quantum chemical and kinetic rate calculations provide important energetic data to evaluate the reaction pathways and isomeric branching Combined experimental and theoretical studies improve the understanding of complex hydrocarbon oxidation reactions

17 Section: Aerosol Cloud-Precipitation Interaction: Facts and Fiction Monday afternoon MCW Level 2 A13C-0925 Simulations of Effects of Aerosols and Relative Humidity on Cumulus Clouds Using Cloud-Resolving Models Presented by Jiwen Fan

18 Section: Tropospheric Heterogeneous Chemistry and Aerosol Phase Transitions Wednesday Afternoon MCW Level 2 A33A-0962 Heterogeneous Chemistry of Carbonyls and Alcohols With Sulfuric Acid: Implications for Secondary rganic Aerosol Formation A33A-0966 Aging of soot by interaction with organic compounds Both presented by Jun Zhao

19 Thank you for your attention! Question?

20

21