1. Week 6. Some Tricks of Doing PES Calculations
PES = Potential Energy Surface

2. 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

3. 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.

4. 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

5. F2 + CH3SCH3  CH3-S-CH2F + HF F  CH3-S=CH2 + HF m80 m20
 CH3SFCH F
m m19
Distinguish Isomers F

6. 8.7 eV
8.7 eV
7.8 eV

7. 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

8. Effect of Basis Sets
F2 +
F +
No aug-basis on F

9. 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

10. 2-D PES with fixed (CH3)2S geometry
F-FS(CH3)2 distance (Å)
FF-S(CH3)2 distance (Å)

11. “safe” ☻ ☹? PE profile on the reaction coordinate (CH3)2S + F2 INT
(CH3)2SF + F ☹?
“safe” ☻

12. 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

13. VDW
F2+
+ F
+ HF
TS1 ≲ -2.5
INT (-12)
3.4 kcal/mol
0.0
TS2
-80.1

14. 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

15. Dipole(z) (atomic unit)
Charge on Fout
TS2
INT
Dipole(z) (atomic unit)
F-H distance (Å)

16. 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

17. Covalent or Ionic? ~ F - TS2 INT CH2SFCH3 F-S=1.792 S-CH3=1.793
∠CSC=103o
∠FS(CH3)=88o
∠FS(CH2)=117o
CH2SFCH3

18. 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

19. One more thing about M-M Reaction

20. 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+

21. H3C S F F S
H3C
Proposed mechanism S F
H3C

22. 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

23. Thank You for Your Attention
Potential Energy Surface
Product Distribution