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Published byΒαρσαββάς Μαυρίδης Modified over 6 years ago
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Week 6. Some Tricks of Doing PES Calculations
PES = Potential Energy Surface
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F2 + CH3SCH3 (DMS) Reaction
Reaction between two Closed Shell molecules J. Chem. Phys. 127, (2007) Usually a closed-shell molecule does not like to react with another closed-shell one. M-M Reaction
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Closed Shell means that
the configuration of doubly occupied molecular orbitals predominate. Usually a molecule with closed shell electronic structure is more stable and easier to be calculated.
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Atom, Molecule & Radical
H C N O F Ne 原子 H C N O F Ne Molecule H2 CH4 NH3 H2O HF H C N H H 2 or 8 electrons (Octet) 分子 H H O H H F Radical H CH3 NH2 OH F 1 or 7 electrons (1 unpaired) テジカル H C H N H O H F Chemical Reaction H H + Cl Cl H + Cl H 化学反应 H + Cl HCl + Cl Cl + H HCl + H
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F2 + CH3SCH3 CH3-S-CH2F + HF F CH3-S=CH2 + HF m80 m20
CH3SFCH F m m19 Distinguish Isomers F
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8.7 eV 8.7 eV 7.8 eV
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3.4 kcal/mol + F F2+ 0.0 TS1 ≲ -2.5 TS2 VDW INT (-12) + HF -80.1
Geometry: CAS-PT2 & QCISD(T) /cc-pVDZ (C,H); cc-pV(T+d)Z (S); aug-cc-pVTZ (F) Energy (kcal/mol): CCSD(T) & CAS-PT2 / Complete Basis Set Extrapolation for S, F. VDW F2+ + F + HF TS1 ≲ -2.5 INT (-12) 3.4 kcal/mol 0.0 TS2 -80.1
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Effect of Basis Sets F2 + F + No aug-basis on F
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Similar (CH3)2S structures
Smaller basis sets for C and H are OK. The error will be canceled in the relative energy. S-C=1.806 ∠CSC=98o 1.42 F2 DMS 1.92 1.78 2.76 1.45 ∠CSF=87o S-C=1.807 ∠CSC=98o ∠SFF=170o ∠SFF=171o ∠CSF=91o S-C=1.794 ∠CSC=100o VDW INT 1.49 2.52 2.00 ∠CSF=90o S-C=1.807 ∠CSC=99o ∠CSF=89o S-C=1.788 ∠CSC=101o ∠SFF=173o (CH3)2SF TS1
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2-D PES with fixed (CH3)2S geometry
F-FS(CH3)2 distance (Å) FF-S(CH3)2 distance (Å)
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“safe” ☻ ☹? PE profile on the reaction coordinate (CH3)2S + F2 INT
(CH3)2SF + F ☹? “safe” ☻
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three-center four-electron bonding
(CH3)2S: n s* e e s F-F three-center four-electron bonding s* e e n e e s INT
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VDW F2+ + F + HF TS1 ≲ -2.5 INT (-12) 3.4 kcal/mol 0.0 TS2 -80.1
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TS2 is Very Special! H-F: 1.95Å Free HF bond distance = 0.92Å
for transition states: typical H-F distance = 1.1~1.4 Å 1.90 1.83 H-F: 1.95Å
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Dipole(z) (atomic unit)
Charge on Fout TS2 INT Dipole(z) (atomic unit) F-H distance (Å)
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Auto Charge Separation (Harpoon) mechanism
F + CH3SFCH3 HF + CH2SFCH3 Vertical IE of CH3SFCH3 = 7.8 eV Electron Affinity of F = 3.5 eV CH3SFCH F- -1/R 4.3 eV 3.4Å CH3SFCH3 + F
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Covalent or Ionic? ~ F - TS2 INT CH2SFCH3 F-S=1.792 S-CH3=1.793
∠CSC=103o ∠FS(CH3)=88o ∠FS(CH2)=117o CH2SFCH3
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最穩定的分子不一定會先形成 F2 + DMS CH3 + 0.0 -14.8 -29.0 CH3 +
Rel. Energy (kcal/mol) -100.6 SF2(CH3)2
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One more thing about M-M Reaction
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F2 + CH3-S-S-CH3 CH3SF + CH3SF, Barrier << 1 kcal/mol
F + CH3-SF-S-CH3 , EC > 4kcal/mol CH3SF+ from CH3S2FCH3 CH3SS(F)CH3+
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H3C S F F S H3C Proposed mechanism S F H3C
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Acknowledgement Exp: Yu-Ju Lu (呂育儒), Lance Lee (李久林), Dr. Chu Shuan Chang (張志鉉), H-J Shao (邵華潔), Chi-Wei Liang (梁記偉), 方靜雯, 陳學穎 Cal: James Pan (潘俊維), Dr. Tingxian Xie (解廷獻), Prof. Henryk Witek Prof. Yuan T. Lee, Prof. Yuan-Pern Lee NSRRC for beam-time and help from Dr. Shih-Huang Lee’s group $$$: Academia Sinica, NSC
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Thank You for Your Attention
Potential Energy Surface Product Distribution
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